[InstCombine] try to reduce x86 addcarry to generic uaddo intrinsic
If we can reduce the x86-specific intrinsic to the generic op, it allows existing
simplifications and value tracking folds. AFAICT, this always results in identical
x86 codegen in the non-reduced case...which should be true because we semi-generically
(too aggressively IMO) convert to llvm.uadd.with.overflow in CGP, so the DAG/isel must
already combine/lower this intrinsic as expected.
This isn't quite what was requested in:
https://bugs.llvm.org/show_bug.cgi?id=40486
...but we want to have these kinds of folds early for efficiency and to enable greater
simplifications. For the case in the bug report where we have:
_addcarry_u64(0, ahi, 0, &ahi)
...this gets completely simplified away in IR.
Differential Revision: https://reviews.llvm.org/D57453
llvm-svn: 352870
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index 7b09fe6..80d1144 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -751,6 +751,33 @@
return nullptr;
}
+static Value *simplifyX86addcarry(const IntrinsicInst &II,
+ InstCombiner::BuilderTy &Builder) {
+ Value *CarryIn = II.getArgOperand(0);
+ Value *Op1 = II.getArgOperand(1);
+ Value *Op2 = II.getArgOperand(2);
+ Type *RetTy = II.getType();
+ Type *OpTy = Op1->getType();
+ assert(RetTy->getStructElementType(0)->isIntegerTy(8) &&
+ RetTy->getStructElementType(1) == OpTy && OpTy == Op2->getType() &&
+ "Unexpected types for x86 addcarry");
+
+ // If carry-in is zero, this is just an unsigned add with overflow.
+ if (match(CarryIn, m_ZeroInt())) {
+ Value *UAdd = Builder.CreateIntrinsic(Intrinsic::uadd_with_overflow, OpTy,
+ { Op1, Op2 });
+ // The types have to be adjusted to match the x86 call types.
+ Value *UAddResult = Builder.CreateExtractValue(UAdd, 0);
+ Value *UAddOV = Builder.CreateZExt(Builder.CreateExtractValue(UAdd, 1),
+ Builder.getInt8Ty());
+ Value *Res = UndefValue::get(II.getType());
+ Res = Builder.CreateInsertValue(Res, UAddOV, 0);
+ return Builder.CreateInsertValue(Res, UAddResult, 1);
+ }
+
+ return nullptr;
+}
+
static Value *simplifyX86insertps(const IntrinsicInst &II,
InstCombiner::BuilderTy &Builder) {
auto *CInt = dyn_cast<ConstantInt>(II.getArgOperand(2));
@@ -3109,6 +3136,12 @@
return nullptr;
break;
+ case Intrinsic::x86_addcarry_32:
+ case Intrinsic::x86_addcarry_64:
+ if (Value *V = simplifyX86addcarry(*II, Builder))
+ return replaceInstUsesWith(*II, V);
+ break;
+
case Intrinsic::ppc_altivec_vperm:
// Turn vperm(V1,V2,mask) -> shuffle(V1,V2,mask) if mask is a constant.
// Note that ppc_altivec_vperm has a big-endian bias, so when creating