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-rw-r--r--compiler/GHC/CmmToAsm/X86/Instr.hs4
1 files changed, 4 insertions, 0 deletions
diff --git a/compiler/GHC/CmmToAsm/X86/Instr.hs b/compiler/GHC/CmmToAsm/X86/Instr.hs
index 1f1515b0c9..42b9543204 100644
--- a/compiler/GHC/CmmToAsm/X86/Instr.hs
+++ b/compiler/GHC/CmmToAsm/X86/Instr.hs
@@ -196,6 +196,10 @@ data Instr
-- Moves.
| MOV Format Operand Operand
+ -- ^ N.B. when used with the 'II64' 'Format', the source
+ -- operand is interpreted to be a 32-bit sign-extended value.
+ -- True 64-bit operands need to be moved with @MOVABS@, which we
+ -- currently don't use.
| CMOV Cond Format Operand Reg
| MOVZxL Format Operand Operand
-- ^ The format argument is the size of operand 1 (the number of bits we keep)