Fix rewriting invalid shifts to errors

Fixes #16449.

5341edf3 removed a code in rewrite rules for bit shifts, which broke the
"silly shift guard", causing generating invalid bit shifts or heap
overflow in compile time while trying to evaluate those invalid bit
shifts.

The "guard" is explained in Note [Guarding against silly shifts] in
PrelRules.hs.

More specifically, this was the breaking change:

    --- a/compiler/prelude/PrelRules.hs
    +++ b/compiler/prelude/PrelRules.hs
    @@ -474,12 +474,11 @@ shiftRule shift_op
            ; case e1 of
                _ | shift_len == 0
                  -> return e1
    -             | shift_len < 0 || wordSizeInBits dflags < shift_len
    -             -> return (mkRuntimeErrorApp rUNTIME_ERROR_ID wordPrimTy
    -                                        ("Bad shift length" ++ show shift_len))

This patch reverts this change.

Two new tests added:

- T16449_1: The original reproducer in #16449. This was previously
  casing a heap overflow in compile time when CmmOpt tries to evaluate
  the large (invalid) bit shift in compile time, using `Integer` as the
  result type. Now it builds as expected. We now generate an error for
  the shift as expected.

- T16449_2: Tests code generator for large (invalid) bit shifts.

6 files changed, 25 insertions, 1 deletions

diff --git a/compiler/prelude/PrelRules.hs b/compiler/prelude/PrelRules.hs
index 7111c7b07a..b0ad91db99 100644
--- a/compiler/prelude/PrelRules.hs
+++ b/compiler/prelude/PrelRules.hs
@@ -467,13 +467,16 @@ shiftRule :: (DynFlags -> Integer -> Int -> Integer) -> RuleM CoreExpr
 -- Used for shift primops
 --    ISllOp, ISraOp, ISrlOp :: Word# -> Int# -> Word#
 --    SllOp, SrlOp           :: Word# -> Int# -> Word#
--- See Note [Guarding against silly shifts]
 shiftRule shift_op
   = do { dflags <- getDynFlags
        ; [e1, Lit (LitNumber LitNumInt shift_len _)] <- getArgs
        ; case e1 of
            _ | shift_len == 0
              -> return e1
+             -- See Note [Guarding against silly shifts]
+             | shift_len < 0 || shift_len > wordSizeInBits dflags
+             -> return $ mkRuntimeErrorApp rUNTIME_ERROR_ID wordPrimTy
+                           ("Bad shift length " ++ show shift_len)
 
            -- Do the shift at type Integer, but shift length is Int
            Lit (LitNumber nt x t)
diff --git a/testsuite/tests/codeGen/should_compile/T16449_1.hs b/testsuite/tests/codeGen/should_compile/T16449_1.hs
new file mode 100644
index 0000000000..b1ec71efef
--- /dev/null
+++ b/testsuite/tests/codeGen/should_compile/T16449_1.hs
@@ -0,0 +1,8 @@
+module T16449_1 where
+
+import Data.Bits (setBit)
+
+f :: Int
+f = foldl setter 0 $ zip [0..] [()]
+  where
+    setter v (ix, _) = setBit v ix
diff --git a/testsuite/tests/codeGen/should_compile/all.T b/testsuite/tests/codeGen/should_compile/all.T
index 7217d93e30..7a9229533d 100644
--- a/testsuite/tests/codeGen/should_compile/all.T
+++ b/testsuite/tests/codeGen/should_compile/all.T
@@ -52,3 +52,5 @@ test('T15723',
   [ unless(have_profiling(), skip),
     unless(have_dynamic(), skip),
   ], run_command, ['$MAKE -s --no-print-directory T15723'])
+
+test('T16449_1', normal, compile, [''])
diff --git a/testsuite/tests/codeGen/should_run/T16449_2.hs b/testsuite/tests/codeGen/should_run/T16449_2.hs
new file mode 100644
index 0000000000..3424d43e25
--- /dev/null
+++ b/testsuite/tests/codeGen/should_run/T16449_2.hs
@@ -0,0 +1,9 @@
+{-# LANGUAGE MagicHash #-}
+
+module Main where
+
+import GHC.Prim
+import GHC.Int
+
+-- Shift should be larger than the word size (e.g. 64 on 64-bit) for this test.
+main = print (I# (uncheckedIShiftL# 1# 1000#))
diff --git a/testsuite/tests/codeGen/should_run/T16449_2.stderr b/testsuite/tests/codeGen/should_run/T16449_2.stderr
new file mode 100644
index 0000000000..869a5b0f91
--- /dev/null
+++ b/testsuite/tests/codeGen/should_run/T16449_2.stderr
@@ -0,0 +1 @@
+T16449_2: Bad shift length 1000
diff --git a/testsuite/tests/codeGen/should_run/all.T b/testsuite/tests/codeGen/should_run/all.T
index 7f976b8107..ade88df6ab 100644
--- a/testsuite/tests/codeGen/should_run/all.T
+++ b/testsuite/tests/codeGen/should_run/all.T
@@ -192,3 +192,4 @@ test('T15892',
         # happen, so -G1 -A32k:
         extra_run_opts('+RTS -G1 -A32k -RTS') ],
      compile_and_run, ['-O'])
+test('T16449_2', exit_code(1), compile_and_run, [''])