[GlobalISel][Legalizer] Fix legalization of llvm.smul.with.overflow
Previously the code for handling G_SMULO didn't properly check for the signed
multiply overflow, instead treating it the same as the unsigned G_UMULO.
Fixes PR35800.
llvm-svn: 321690
diff --git a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
index a3b43c9..c711820 100644
--- a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -813,7 +813,21 @@
unsigned Zero = MRI.createGenericVirtualRegister(Ty);
MIRBuilder.buildConstant(Zero, 0);
- MIRBuilder.buildICmp(CmpInst::ICMP_NE, Overflow, HiPart, Zero);
+
+ // For *signed* multiply, overflow is detected by checking:
+ // (hi != (lo >> bitwidth-1))
+ if (Opcode == TargetOpcode::G_SMULH) {
+ unsigned Shifted = MRI.createGenericVirtualRegister(Ty);
+ unsigned ShiftAmt = MRI.createGenericVirtualRegister(Ty);
+ MIRBuilder.buildConstant(ShiftAmt, Ty.getSizeInBits() - 1);
+ MIRBuilder.buildInstr(TargetOpcode::G_ASHR)
+ .addDef(Shifted)
+ .addUse(Res)
+ .addUse(ShiftAmt);
+ MIRBuilder.buildICmp(CmpInst::ICMP_NE, Overflow, HiPart, Shifted);
+ } else {
+ MIRBuilder.buildICmp(CmpInst::ICMP_NE, Overflow, HiPart, Zero);
+ }
MI.eraseFromParent();
return Legalized;
}