X86InstrInfo: Support immediates that are +1/-1 different in optimizeCompareInstroptimize_compinstr_fix

This is a re-commit of e2c7ee0743592e39274e28dbe0d0c213ba342317 which
was reverted in a2a58d91e82db38fbdf88cc317dcb3753d79d492 and
ea81cea8163a1a0e54df42103ee1c657bbf03791. This includes a fix to
consistently check for EFLAGS being live-out. See phabricator
review.

Original Summary:

This extends `optimizeCompareInstr` to re-use previous comparison
results if the previous comparison was with an immediate that was 1
bigger or smaller. Example:

    CMP x, 13
    ...
    CMP x, 12   ; can be removed if we change the SETg
    SETg ...    ; x > 12  changed to `SETge` (x >= 13) removing CMP

Motivation: This often happens because SelectionDAG canonicalization
tends to add/subtract 1 often when optimizing for fallthrough blocks.
Example for `x > C` the fallthrough optimization switches true/false
blocks with `!(x > C)` --> `x <= C` and canonicalization turns this into
`x < C + 1`.

Differential Revision: https://reviews.llvm.org/D110867

5 files changed, 497 insertions, 24 deletions

diff --git a/llvm/lib/Target/X86/X86InstrInfo.cpp b/llvm/lib/Target/X86/X86InstrInfo.cpp
index c379aa8d9258..4dcd886fa3b2 100644
--- a/llvm/lib/Target/X86/X86InstrInfo.cpp
+++ b/llvm/lib/Target/X86/X86InstrInfo.cpp
@@ -4088,8 +4088,8 @@ bool X86InstrInfo::analyzeCompare(const MachineInstr &MI, Register &SrcReg,
 bool X86InstrInfo::isRedundantFlagInstr(const MachineInstr &FlagI,
                                         Register SrcReg, Register SrcReg2,
                                         int64_t ImmMask, int64_t ImmValue,
-                                        const MachineInstr &OI,
-                                        bool *IsSwapped) const {
+                                        const MachineInstr &OI, bool *IsSwapped,
+                                        int64_t *ImmDelta) const {
   switch (OI.getOpcode()) {
   case X86::CMP64rr:
   case X86::CMP32rr:
@@ -4140,10 +4140,21 @@ bool X86InstrInfo::isRedundantFlagInstr(const MachineInstr &FlagI,
       int64_t OIMask;
       int64_t OIValue;
       if (analyzeCompare(OI, OISrcReg, OISrcReg2, OIMask, OIValue) &&
-          SrcReg == OISrcReg && ImmMask == OIMask && OIValue == ImmValue) {
-        assert(SrcReg2 == X86::NoRegister && OISrcReg2 == X86::NoRegister &&
-               "should not have 2nd register");
-        return true;
+          SrcReg == OISrcReg && ImmMask == OIMask) {
+        if (OIValue == ImmValue) {
+          *ImmDelta = 0;
+          return true;
+        } else if (static_cast<uint64_t>(ImmValue) ==
+                   static_cast<uint64_t>(OIValue) - 1) {
+          *ImmDelta = -1;
+          return true;
+        } else if (static_cast<uint64_t>(ImmValue) ==
+                   static_cast<uint64_t>(OIValue) + 1) {
+          *ImmDelta = 1;
+          return true;
+        } else {
+          return false;
+        }
       }
     }
     return FlagI.isIdenticalTo(OI);
@@ -4393,6 +4404,7 @@ bool X86InstrInfo::optimizeCompareInstr(MachineInstr &CmpInstr, Register SrcReg,
   bool ShouldUpdateCC = false;
   bool IsSwapped = false;
   X86::CondCode NewCC = X86::COND_INVALID;
+  int64_t ImmDelta = 0;
 
   // Search backward from CmpInstr for the next instruction defining EFLAGS.
   const TargetRegisterInfo *TRI = &getRegisterInfo();
@@ -4439,7 +4451,7 @@ bool X86InstrInfo::optimizeCompareInstr(MachineInstr &CmpInstr, Register SrcReg,
         //     ...           // EFLAGS not changed
         //     cmp x, y      // <-- can be removed
         if (isRedundantFlagInstr(CmpInstr, SrcReg, SrcReg2, CmpMask, CmpValue,
-                                 Inst, &IsSwapped)) {
+                                 Inst, &IsSwapped, &ImmDelta)) {
           Sub = &Inst;
           break;
         }
@@ -4473,7 +4485,7 @@ bool X86InstrInfo::optimizeCompareInstr(MachineInstr &CmpInstr, Register SrcReg,
   // It is safe to remove CmpInstr if EFLAGS is redefined or killed.
   // If we are done with the basic block, we need to check whether EFLAGS is
   // live-out.
-  bool IsSafe = false;
+  bool FlagsMayLiveOut = true;
   SmallVector<std::pair<MachineInstr*, X86::CondCode>, 4> OpsToUpdate;
   MachineBasicBlock::iterator AfterCmpInstr =
       std::next(MachineBasicBlock::iterator(CmpInstr));
@@ -4483,7 +4495,7 @@ bool X86InstrInfo::optimizeCompareInstr(MachineInstr &CmpInstr, Register SrcReg,
     // We should check the usage if this instruction uses and updates EFLAGS.
     if (!UseEFLAGS && ModifyEFLAGS) {
       // It is safe to remove CmpInstr if EFLAGS is updated again.
-      IsSafe = true;
+      FlagsMayLiveOut = false;
       break;
     }
     if (!UseEFLAGS && !ModifyEFLAGS)
@@ -4491,7 +4503,7 @@ bool X86InstrInfo::optimizeCompareInstr(MachineInstr &CmpInstr, Register SrcReg,
 
     // EFLAGS is used by this instruction.
     X86::CondCode OldCC = X86::COND_INVALID;
-    if (MI || IsSwapped) {
+    if (MI || IsSwapped || ImmDelta != 0) {
       // We decode the condition code from opcode.
       if (Instr.isBranch())
         OldCC = X86::getCondFromBranch(Instr);
@@ -4545,9 +4557,59 @@ bool X86InstrInfo::optimizeCompareInstr(MachineInstr &CmpInstr, Register SrcReg,
       ReplacementCC = getSwappedCondition(OldCC);
       if (ReplacementCC == X86::COND_INVALID)
         return false;
+      ShouldUpdateCC = true;
+    } else if (ImmDelta != 0) {
+      unsigned BitWidth = TRI->getRegSizeInBits(*MRI->getRegClass(SrcReg));
+      // Shift amount for min/max constants to adjust for 8/16/32 instruction
+      // sizes.
+      switch (OldCC) {
+      case X86::COND_L: // x <s (C + 1)  -->  x <=s C
+        if (ImmDelta != 1 || APInt::getSignedMinValue(BitWidth) == CmpValue)
+          return false;
+        ReplacementCC = X86::COND_LE;
+        break;
+      case X86::COND_B: // x <u (C + 1)  -->  x <=u C
+        if (ImmDelta != 1 || CmpValue == 0)
+          return false;
+        ReplacementCC = X86::COND_BE;
+        break;
+      case X86::COND_GE: // x >=s (C + 1)  -->  x >s C
+        if (ImmDelta != 1 || APInt::getSignedMinValue(BitWidth) == CmpValue)
+          return false;
+        ReplacementCC = X86::COND_G;
+        break;
+      case X86::COND_AE: // x >=u (C + 1)  -->  x >u C
+        if (ImmDelta != 1 || CmpValue == 0)
+          return false;
+        ReplacementCC = X86::COND_A;
+        break;
+      case X86::COND_G: // x >s (C - 1)  -->  x >=s C
+        if (ImmDelta != -1 || APInt::getSignedMaxValue(BitWidth) == CmpValue)
+          return false;
+        ReplacementCC = X86::COND_GE;
+        break;
+      case X86::COND_A: // x >u (C - 1)  -->  x >=u C
+        if (ImmDelta != -1 || APInt::getMaxValue(BitWidth) == CmpValue)
+          return false;
+        ReplacementCC = X86::COND_AE;
+        break;
+      case X86::COND_LE: // x <=s (C - 1)  -->  x <s C
+        if (ImmDelta != -1 || APInt::getSignedMaxValue(BitWidth) == CmpValue)
+          return false;
+        ReplacementCC = X86::COND_L;
+        break;
+      case X86::COND_BE: // x <=u (C - 1)  -->  x <u C
+        if (ImmDelta != -1 || APInt::getMaxValue(BitWidth) == CmpValue)
+          return false;
+        ReplacementCC = X86::COND_B;
+        break;
+      default:
+        return false;
+      }
+      ShouldUpdateCC = true;
     }
 
-    if ((ShouldUpdateCC || IsSwapped) && ReplacementCC != OldCC) {
+    if (ShouldUpdateCC && ReplacementCC != OldCC) {
       // Push the MachineInstr to OpsToUpdate.
       // If it is safe to remove CmpInstr, the condition code of these
       // instructions will be modified.
@@ -4555,14 +4617,14 @@ bool X86InstrInfo::optimizeCompareInstr(MachineInstr &CmpInstr, Register SrcReg,
     }
     if (ModifyEFLAGS || Instr.killsRegister(X86::EFLAGS, TRI)) {
       // It is safe to remove CmpInstr if EFLAGS is updated again or killed.
-      IsSafe = true;
+      FlagsMayLiveOut = false;
       break;
     }
   }
 
-  // If EFLAGS is not killed nor re-defined, we should check whether it is
-  // live-out. If it is live-out, do not optimize.
-  if ((MI || IsSwapped) && !IsSafe) {
+  // If we have to update users but EFLAGS is live-out abort, since we cannot
+  // easily find all of the users.
+  if ((MI != nullptr || ShouldUpdateCC) && FlagsMayLiveOut) {
     for (MachineBasicBlock *Successor : CmpMBB.successors())
       if (Successor->isLiveIn(X86::EFLAGS))
         return false;
diff --git a/llvm/lib/Target/X86/X86InstrInfo.h b/llvm/lib/Target/X86/X86InstrInfo.h
index 537ada6222bf..33ce55bbdb2b 100644
--- a/llvm/lib/Target/X86/X86InstrInfo.h
+++ b/llvm/lib/Target/X86/X86InstrInfo.h
@@ -643,7 +643,8 @@ private:
   ///   CMP %1, %2   and  %3 = SUB %2, %1  ; IsSwapped=true
   bool isRedundantFlagInstr(const MachineInstr &FlagI, Register SrcReg,
                             Register SrcReg2, int64_t ImmMask, int64_t ImmValue,
-                            const MachineInstr &OI, bool *IsSwapped) const;
+                            const MachineInstr &OI, bool *IsSwapped,
+                            int64_t *ImmDelta) const;
 };
 
 } // namespace llvm
diff --git a/llvm/test/CodeGen/X86/optimize-compare.mir b/llvm/test/CodeGen/X86/optimize-compare.mir
index dc15cbbab8b1..042d9a5d4384 100644
--- a/llvm/test/CodeGen/X86/optimize-compare.mir
+++ b/llvm/test/CodeGen/X86/optimize-compare.mir
@@ -379,3 +379,361 @@ body: |
     CMP64ri32 %0, 24, implicit-def $eflags
     $cl = SETCCr 3, implicit $eflags
 ...
+---
+name: opt_redundant_flags_adjusted_imm_0
+body: |
+  bb.0:
+    ; CHECK-LABEL: name: opt_redundant_flags_adjusted_imm_0
+    ; CHECK: [[COPY:%[0-9]+]]:gr64 = COPY $rsi
+    ; CHECK-NEXT: CMP64ri8 [[COPY]], 1, implicit-def $eflags
+    ; CHECK-NEXT: $cl = SETCCr 4, implicit $eflags
+    ; CHECK-NEXT: $bl = SETCCr 15, implicit $eflags
+    ; CHECK-NEXT: $bl = SETCCr 7, implicit $eflags
+    ; CHECK-NEXT: $bl = SETCCr 14, implicit $eflags
+    ; CHECK-NEXT: $bl = SETCCr 6, implicit $eflags
+    %0:gr64 = COPY $rsi
+    ; CMP+SETCC   %0 == 1
+    CMP64ri8 %0, 1, implicit-def $eflags
+    $cl = SETCCr 4, implicit $eflags
+    ; CMP+SETCC   %0 >= 2; CMP can be removed.
+    CMP64ri8 %0, 2, implicit-def $eflags
+    ; %0 >=s 2  -->  %0 >s 1
+    $bl = SETCCr 13, implicit $eflags
+    ; %0 >=u 2  -->  %0 >u 1
+    $bl = SETCCr 3, implicit $eflags
+    ; %0 <s 2  -->  %0 <=s 1
+    $bl = SETCCr 12, implicit $eflags
+    ; %0 <u 2  -->  %0 <=u 1
+    $bl = SETCCr 2, implicit $eflags
+...
+---
+name: opt_redundant_flags_adjusted_imm_1
+body: |
+  bb.0:
+    ; CHECK-LABEL: name: opt_redundant_flags_adjusted_imm_1
+    ; CHECK: [[COPY:%[0-9]+]]:gr64 = COPY $rsi
+    ; CHECK-NEXT: CMP64ri8 [[COPY]], 42, implicit-def $eflags
+    ; CHECK-NEXT: $cl = SETCCr 5, implicit $eflags
+    ; CHECK-NEXT: $bl = SETCCr 13, implicit $eflags
+    ; CHECK-NEXT: $bl = SETCCr 3, implicit $eflags
+    ; CHECK-NEXT: $bl = SETCCr 12, implicit $eflags
+    ; CHECK-NEXT: $bl = SETCCr 2, implicit $eflags
+    %0:gr64 = COPY $rsi
+    ; CMP+SETCC   %0 != 42
+    CMP64ri8 %0, 42, implicit-def $eflags
+    $cl = SETCCr 5, implicit $eflags
+    ; CMP+SETCC   %0 >= 2; CMP can be removed.
+    CMP64ri8 %0, 41, implicit-def $eflags
+    ; %0 >s 41  -->  %0 >=s 42
+    $bl = SETCCr 15, implicit $eflags
+    ; %0 >u 41  -->  %0 >=u 42
+    $bl = SETCCr 7, implicit $eflags
+    ; %0 <=s 41  -->  %0 <s 42
+    $bl = SETCCr 14, implicit $eflags
+    ; %0 <=u 41  -->  %0 <u 42
+    $bl = SETCCr 6, implicit $eflags
+...
+---
+name: opt_redundant_flags_adjusted_imm_test_cmp
+body: |
+  bb.0:
+    ; CHECK-LABEL: name: opt_redundant_flags_adjusted_imm_test_cmp
+    ; CHECK: [[COPY:%[0-9]+]]:gr8 = COPY $bl
+    ; CHECK-NEXT: TEST8rr [[COPY]], [[COPY]], implicit-def $eflags
+    ; CHECK-NEXT: $cl = SETCCr 14, implicit $eflags
+    ; CHECK-NEXT: $cl = SETCCr 7, implicit $eflags
+    ; CHECK-NEXT: $cl = SETCCr 12, implicit $eflags
+    %0:gr8 = COPY $bl
+    TEST8rr %0, %0, implicit-def $eflags
+    ; SET %0 <=s 0
+    $cl = SETCCr 14, implicit $eflags
+    ; CMP should be removed (%0 >=u 1)
+    CMP8ri %0, 1, implicit-def $eflags
+    $cl = SETCCr 3, implicit $eflags
+
+    ; CMP should be removed (%0 <=s -1)
+    CMP8ri %0, -1, implicit-def $eflags
+    $cl = SETCCr 14, implicit $eflags
+...
+---
+name: opt_redundant_flags_adjusted_imm_cmp_test
+body: |
+  bb.0:
+    ; CHECK-LABEL: name: opt_redundant_flags_adjusted_imm_cmp_test
+    ; CHECK: [[COPY:%[0-9]+]]:gr64 = COPY $rsi
+    ; CHECK-NEXT: CMP64ri32 [[COPY]], 1, implicit-def $eflags
+    ; CHECK-NEXT: $cl = SETCCr 13, implicit $eflags
+    ; CHECK-NEXT: [[COPY1:%[0-9]+]]:gr64 = COPY $edi
+    ; CHECK-NEXT: CMP64ri32 [[COPY1]], -1, implicit-def $eflags
+    ; CHECK-NEXT: $cl = SETCCr 14, implicit $eflags
+    %0:gr64 = COPY $rsi
+    CMP64ri32 %0, 1, implicit-def $eflags
+    ; TEST should be removed
+    TEST64rr %0, %0, implicit-def $eflags
+    $cl = SETCCr 15, implicit $eflags
+
+    %1:gr64 = COPY $edi
+    CMP64ri32 %1, -1, implicit-def $eflags
+    ; TEST should be removed
+    TEST64rr %1, %1, implicit-def $eflags
+    $cl = SETCCr 12, implicit $eflags
+...
+---
+name: opt_redundant_flags_adjusted_imm_noopt_0
+body: |
+  bb.0:
+    ; CHECK-LABEL: name: opt_redundant_flags_adjusted_imm_noopt_0
+    ; CHECK: [[COPY:%[0-9]+]]:gr64 = COPY $rsi
+    ; CHECK-NEXT: CMP64ri8 [[COPY]], 42, implicit-def $eflags
+    ; CHECK-NEXT: $cl = SETCCr 4, implicit $eflags
+    ; CHECK-NEXT: CMP64ri8 [[COPY]], 41, implicit-def $eflags
+    ; CHECK-NEXT: $bl = SETCCr 4, implicit $eflags
+    %0:gr64 = COPY $rsi
+    ; CMP+SETCC   %0 <s 1
+    CMP64ri8 %0, 42, implicit-def $eflags
+    $cl = SETCCr 4, implicit $eflags
+    ; CMP should not be removed.
+    CMP64ri8 %0, 41, implicit-def $eflags
+    ; %0 == 41
+    $bl = SETCCr 4, implicit $eflags
+...
+---
+name: opt_redundant_flags_adjusted_imm_noopt_1
+body: |
+  bb.0:
+    ; CHECK-LABEL: name: opt_redundant_flags_adjusted_imm_noopt_1
+    ; CHECK: [[COPY:%[0-9]+]]:gr32 = COPY $esi
+    ; CHECK-NEXT: CMP32ri [[COPY]], 2147483647, implicit-def $eflags
+    ; CHECK-NEXT: CMP32ri [[COPY]], -2147483648, implicit-def $eflags
+    ; CHECK-NEXT: $bl = SETCCr 12, implicit $eflags
+    ; CHECK-NEXT: CMP32ri [[COPY]], 4294967295, implicit-def $eflags
+    ; CHECK-NEXT: CMP32ri [[COPY]], -2147483648, implicit-def $eflags
+    ; CHECK-NEXT: $bl = SETCCr 12, implicit $eflags
+    ; CHECK-NEXT: CMP32ri [[COPY]], 2147483647, implicit-def $eflags
+    ; CHECK-NEXT: CMP32ri [[COPY]], -2147483648, implicit-def $eflags
+    ; CHECK-NEXT: $bl = SETCCr 13, implicit $eflags
+    ; CHECK-NEXT: CMP32ri [[COPY]], 4294967295, implicit-def $eflags
+    ; CHECK-NEXT: CMP32ri [[COPY]], 0, implicit-def $eflags
+    ; CHECK-NEXT: $bl = SETCCr 2, implicit $eflags
+    ; CHECK-NEXT: CMP32ri [[COPY]], 4294967295, implicit-def $eflags
+    ; CHECK-NEXT: CMP32ri [[COPY]], 0, implicit-def $eflags
+    ; CHECK-NEXT: $bl = SETCCr 3, implicit $eflags
+    %0:gr32 = COPY $esi
+    ; CMP+SETCC   %0 == INT32_MAX
+    CMP32ri %0, 2147483647, implicit-def $eflags
+    ; CMP should not be removed.
+    CMP32ri %0, -2147483648, implicit-def $eflags
+    ; %0 <s INT32_MIN
+    $bl = SETCCr 12, implicit $eflags
+
+    CMP32ri %0, 4294967295, implicit-def $eflags
+    ; CMP should not be removed.
+    CMP32ri %0, -2147483648, implicit-def $eflags
+    $bl = SETCCr 12, implicit $eflags
+
+    CMP32ri %0, 2147483647, implicit-def $eflags
+    ; CMP should not be removed.
+    CMP32ri %0, -2147483648, implicit-def $eflags
+    $bl = SETCCr 13, implicit $eflags
+
+    CMP32ri %0, 4294967295, implicit-def $eflags
+    ; should not be removed
+    CMP32ri %0, 0, implicit-def $eflags
+    $bl = SETCCr 2, implicit $eflags
+
+    CMP32ri %0, 4294967295, implicit-def $eflags
+    ; should not be removed
+    CMP32ri %0, 0, implicit-def $eflags
+    $bl = SETCCr 3, implicit $eflags
+...
+---
+name: opt_redundant_flags_adjusted_imm_noopt_2
+body: |
+  bb.0:
+    ; CHECK-LABEL: name: opt_redundant_flags_adjusted_imm_noopt_2
+    ; CHECK: [[COPY:%[0-9]+]]:gr16 = COPY $cx
+    ; CHECK-NEXT: CMP16ri [[COPY]], -32768, implicit-def $eflags
+    ; CHECK-NEXT: CMP16ri [[COPY]], 32767, implicit-def $eflags
+    ; CHECK-NEXT: $bl = SETCCr 15, implicit $eflags
+    ; CHECK-NEXT: CMP16ri [[COPY]], 65535, implicit-def $eflags
+    ; CHECK-NEXT: CMP16ri [[COPY]], 32767, implicit-def $eflags
+    ; CHECK-NEXT: $bl = SETCCr 15, implicit $eflags
+    ; CHECK-NEXT: CMP16ri [[COPY]], -32768, implicit-def $eflags
+    ; CHECK-NEXT: CMP16ri [[COPY]], 32767, implicit-def $eflags
+    ; CHECK-NEXT: $bl = SETCCr 14, implicit $eflags
+    ; CHECK-NEXT: CMP16ri [[COPY]], 0, implicit-def $eflags
+    ; CHECK-NEXT: CMP16ri [[COPY]], 65535, implicit-def $eflags
+    ; CHECK-NEXT: $bl = SETCCr 4, implicit $eflags
+    ; CHECK-NEXT: CMP16ri [[COPY]], 0, implicit-def $eflags
+    ; CHECK-NEXT: CMP16ri [[COPY]], 65535, implicit-def $eflags
+    ; CHECK-NEXT: $bl = SETCCr 6, implicit $eflags
+    %0:gr16 = COPY $cx
+    ; CMP+SETCC   %0 == INT16_MIN
+    CMP16ri %0, -32768, implicit-def $eflags
+    ; CMP should not be removed.
+    CMP16ri %0, 32767, implicit-def $eflags
+    ; %0 >s INT16_MAX
+    $bl = SETCCr 15, implicit $eflags
+
+    CMP16ri %0, 65535, implicit-def $eflags
+    ; CMP should not be removed.
+    CMP16ri %0, 32767, implicit-def $eflags
+    $bl = SETCCr 15, implicit $eflags
+
+    CMP16ri %0, -32768, implicit-def $eflags
+    ; CMP should not be removed.
+    CMP16ri %0, 32767, implicit-def $eflags
+    $bl = SETCCr 14, implicit $eflags
+
+    CMP16ri %0, 0, implicit-def $eflags
+    ; should not be removed
+    CMP16ri %0, 65535, implicit-def $eflags
+    $bl = SETCCr 4, implicit $eflags
+
+    CMP16ri %0, 0, implicit-def $eflags
+    ; should not be removed
+    CMP16ri %0, 65535, implicit-def $eflags
+    $bl = SETCCr 6, implicit $eflags
+...
+---
+name: opt_adjusted_imm_multiple_blocks
+body: |
+  ; CHECK-LABEL: name: opt_adjusted_imm_multiple_blocks
+  ; CHECK: bb.0:
+  ; CHECK-NEXT:   successors: %bb.1(0x40000000), %bb.3(0x40000000)
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   [[COPY:%[0-9]+]]:gr32 = COPY $eax
+  ; CHECK-NEXT:   CMP32ri [[COPY]], 20, implicit-def $eflags
+  ; CHECK-NEXT:   JCC_1 %bb.1, 4, implicit $eflags
+  ; CHECK-NEXT:   JMP_1 %bb.3
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.1:
+  ; CHECK-NEXT:   successors: %bb.2(0x40000000), %bb.3(0x40000000)
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   JCC_1 %bb.2, 15, implicit $eflags
+  ; CHECK-NEXT:   JMP_1 %bb.3
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.2:
+  ; CHECK-NEXT:   successors: %bb.3(0x80000000)
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   JMP_1 %bb.3
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.3:
+  ; CHECK-NEXT:   RET 0
+  bb.0:
+    %0:gr32 = COPY $eax
+    CMP32ri %0, 20, implicit-def $eflags
+    JCC_1 %bb.1, 4, implicit $eflags
+    JMP_1 %bb.3
+
+  bb.1:
+    ; CMP can be removed when adjusting the JCC.
+    CMP32ri %0, 21, implicit-def $eflags
+    JCC_1 %bb.2, 13, implicit $eflags
+    JMP_1 %bb.3
+
+  bb.2:
+    JMP_1 %bb.3
+
+  bb.3:
+    RET 0
+...
+---
+name: opt_adjusted_imm_multiple_blocks_noopt
+body: |
+  ; CHECK-LABEL: name: opt_adjusted_imm_multiple_blocks_noopt
+  ; CHECK: bb.0:
+  ; CHECK-NEXT:   successors: %bb.1(0x40000000), %bb.3(0x40000000)
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   [[COPY:%[0-9]+]]:gr32 = COPY $eax
+  ; CHECK-NEXT:   CMP32ri [[COPY]], 20, implicit-def $eflags
+  ; CHECK-NEXT:   JCC_1 %bb.1, 4, implicit $eflags
+  ; CHECK-NEXT:   JMP_1 %bb.3
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.1:
+  ; CHECK-NEXT:   successors: %bb.2(0x40000000), %bb.3(0x40000000)
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   CMP32ri [[COPY]], 21, implicit-def $eflags
+  ; CHECK-NEXT:   JCC_1 %bb.2, 13, implicit $eflags
+  ; CHECK-NEXT:   JMP_1 %bb.3
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.2:
+  ; CHECK-NEXT:   successors: %bb.3(0x80000000)
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   $al = SETCCr 4, implicit $eflags
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.3:
+  ; CHECK-NEXT:   RET 0
+  bb.0:
+    %0:gr32 = COPY $eax
+    CMP32ri %0, 20, implicit-def $eflags
+    JCC_1 %bb.1, 4, implicit $eflags
+    JMP_1 %bb.3
+
+  bb.1:
+    ; The following CMP should not be optimized because $eflags is live-out
+    CMP32ri %0, 21, implicit-def $eflags
+    JCC_1 %bb.2, 13, implicit $eflags
+    JMP_1 %bb.3
+
+  bb.2:
+    liveins: $eflags
+    $al = SETCCr 4, implicit $eflags
+
+  bb.3:
+    RET 0
+...
+---
+name: opt_shift_cmp_zero
+body: |
+  bb.0:
+    ; CHECK-LABEL: name: opt_shift_cmp_zero
+    ; CHECK: [[COPY:%[0-9]+]]:gr64 = COPY $rsi
+    ; CHECK-NEXT: [[SHL64ri:%[0-9]+]]:gr64 = SHL64ri [[COPY]], 7, implicit-def $eflags
+    ; CHECK-NEXT: $al = SETCCr 4, implicit $eflags
+    %0:gr64 = COPY $rsi
+    %1:gr64 = SHL64ri %0, 7, implicit-def dead $eflags
+    ; TEST should be removed.
+    TEST64rr %1, %1, implicit-def $eflags
+    $al = SETCCr 4, implicit $eflags
+...
+---
+name: noopt_shift_cmp_zero
+body: |
+  bb.0:
+    ; CHECK-LABEL: name: noopt_shift_cmp_zero
+    ; CHECK: [[COPY:%[0-9]+]]:gr64 = COPY $rsi
+    ; CHECK-NEXT: [[SHL64ri:%[0-9]+]]:gr64 = SHL64ri [[COPY]], 9, implicit-def dead $eflags
+    ; CHECK-NEXT: TEST64rr [[SHL64ri]], [[SHL64ri]], implicit-def $eflags
+    ; CHECK-NEXT: $al = SETCCr 14, implicit $eflags
+    %0:gr64 = COPY $rsi
+    %1:gr64 = SHL64ri %0, 9, implicit-def dead $eflags
+    ; TEST cannot be removed if a user relies on the OF flag.
+    TEST64rr %1, %1, implicit-def $eflags
+    $al = SETCCr 14, implicit $eflags
+...
+---
+name: noopt_shift_cmp_zero_multiblock
+body: |
+  ; CHECK-LABEL: name: noopt_shift_cmp_zero_multiblock
+  ; CHECK: bb.0:
+  ; CHECK-NEXT:   successors: %bb.1(0x80000000)
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   [[COPY:%[0-9]+]]:gr64 = COPY $rsi
+  ; CHECK-NEXT:   [[SHL64ri:%[0-9]+]]:gr64 = SHL64ri [[COPY]], 9, implicit-def dead $eflags
+  ; CHECK-NEXT:   TEST64rr [[SHL64ri]], [[SHL64ri]], implicit-def $eflags
+  ; CHECK-NEXT:   JMP_1 %bb.1
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.1:
+  ; CHECK-NEXT:   $al = SETCCr 14, implicit $eflags
+  bb.0:
+    %0:gr64 = COPY $rsi
+    %1:gr64 = SHL64ri %0, 9, implicit-def dead $eflags
+    ; TEST cannot be removed if a user relies on the OF flag.
+    TEST64rr %1, %1, implicit-def $eflags
+    JMP_1 %bb.1
+
+  bb.1:
+    liveins: $eflags
+    $al = SETCCr 14, implicit $eflags
+...
diff --git a/llvm/test/CodeGen/X86/peep-test-5.ll b/llvm/test/CodeGen/X86/peep-test-5.ll
new file mode 100644
index 000000000000..2530cf6576b8
--- /dev/null
+++ b/llvm/test/CodeGen/X86/peep-test-5.ll
@@ -0,0 +1,56 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -o - %s -mtriple=x86_64-- | FileCheck %s
+; Example of a decref operation with "immortal" objects.
+; void decref(long* refcount) {
+;  long count = *refcount;
+;  if (count == 1) { free_object() }
+;  else if (count > 1) { *refcount = count - 1; }
+;  else { /* immortal */ }
+; }
+; Resulting assembly should share flags from single CMP instruction for both
+; conditions!
+define void @decref(i32* %p) {
+; CHECK-LABEL: decref:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    pushq %rax
+; CHECK-NEXT:    .cfi_def_cfa_offset 16
+; CHECK-NEXT:    movl (%rdi), %eax
+; CHECK-NEXT:    cmpl $1, %eax
+; CHECK-NEXT:    jne .LBB0_2
+; CHECK-NEXT:  # %bb.1: # %bb_free
+; CHECK-NEXT:    callq free_object@PLT
+; CHECK-NEXT:  .LBB0_4: # %end
+; CHECK-NEXT:    popq %rax
+; CHECK-NEXT:    .cfi_def_cfa_offset 8
+; CHECK-NEXT:    retq
+; CHECK-NEXT:  .LBB0_2: # %bb2
+; CHECK-NEXT:    .cfi_def_cfa_offset 16
+; CHECK-NEXT:    jle .LBB0_4
+; CHECK-NEXT:  # %bb.3: # %bb_dec
+; CHECK-NEXT:    decl %eax
+; CHECK-NEXT:    movl %eax, (%rdi)
+; CHECK-NEXT:    popq %rax
+; CHECK-NEXT:    .cfi_def_cfa_offset 8
+; CHECK-NEXT:    retq
+  %count = load i32, i32* %p, align 4
+  %cmp0 = icmp eq i32 %count, 1
+  br i1 %cmp0, label %bb_free, label %bb2
+
+bb2:
+  %cmp1 = icmp sgt i32 %count, 1
+  br i1 %cmp1, label %bb_dec, label %end
+
+bb_dec:
+  %dec = add nsw i32 %count, -1
+  store i32 %dec, i32* %p, align 4
+  br label %end
+
+bb_free:
+  call void @free_object()
+  br label %end
+
+end:
+  ret void
+}
+
+declare void @free_object()
diff --git a/llvm/test/CodeGen/X86/use-cr-result-of-dom-icmp-st.ll b/llvm/test/CodeGen/X86/use-cr-result-of-dom-icmp-st.ll
index baae1ab539e0..ae25f0522575 100644
--- a/llvm/test/CodeGen/X86/use-cr-result-of-dom-icmp-st.ll
+++ b/llvm/test/CodeGen/X86/use-cr-result-of-dom-icmp-st.ll
@@ -117,9 +117,8 @@ define i64 @ll_a_op_b_1(i64 %a, i64 %b) {
 ; CHECK-NEXT:    cmpq $1, %rdx
 ; CHECK-NEXT:    jg .LBB3_2
 ; CHECK-NEXT:  # %bb.1: # %if.end
-; CHECK-NEXT:    testq %rdx, %rdx
 ; CHECK-NEXT:    movl $1, %ecx
-; CHECK-NEXT:    cmovleq %rcx, %rax
+; CHECK-NEXT:    cmovlq %rcx, %rax
 ; CHECK-NEXT:    imulq %rdi, %rax
 ; CHECK-NEXT:  .LBB3_2: # %return
 ; CHECK-NEXT:    retq
@@ -256,9 +255,8 @@ define i64 @ll_a_1(i64 %a, i64 %b) {
 ; CHECK-NEXT:    cmpq $1, %rdi
 ; CHECK-NEXT:    jg .LBB8_2
 ; CHECK-NEXT:  # %bb.1: # %if.end
-; CHECK-NEXT:    testq %rdi, %rdi
 ; CHECK-NEXT:    movl $1, %ecx
-; CHECK-NEXT:    cmovleq %rcx, %rax
+; CHECK-NEXT:    cmovlq %rcx, %rax
 ; CHECK-NEXT:    imulq %rdi, %rax
 ; CHECK-NEXT:  .LBB8_2: # %return
 ; CHECK-NEXT:    retq
@@ -412,9 +410,8 @@ define i64 @i_a_op_b_1(i32 signext %a, i32 signext %b) {
 ; CHECK-NEXT:    cmpl $1, %eax
 ; CHECK-NEXT:    jg .LBB13_2
 ; CHECK-NEXT:  # %bb.1: # %if.end
-; CHECK-NEXT:    testl %eax, %eax
 ; CHECK-NEXT:    movl $1, %eax
-; CHECK-NEXT:    cmovlel %eax, %ecx
+; CHECK-NEXT:    cmovll %eax, %ecx
 ; CHECK-NEXT:    imull %edi, %ecx
 ; CHECK-NEXT:  .LBB13_2: # %return
 ; CHECK-NEXT:    movslq %ecx, %rax
@@ -563,9 +560,8 @@ define i64 @i_a_1(i32 signext %a, i32 signext %b) {
 ; CHECK-NEXT:    cmpl $1, %edi
 ; CHECK-NEXT:    jg .LBB18_2
 ; CHECK-NEXT:  # %bb.1: # %if.end
-; CHECK-NEXT:    testl %edi, %edi
 ; CHECK-NEXT:    movl $1, %eax
-; CHECK-NEXT:    cmovlel %eax, %esi
+; CHECK-NEXT:    cmovll %eax, %esi
 ; CHECK-NEXT:    imull %edi, %esi
 ; CHECK-NEXT:  .LBB18_2: # %return
 ; CHECK-NEXT:    movslq %esi, %rax