[InstCombine] fold adds of constants separated by sext/zext
This is part of a transform that may be done in the backend:
D13757
...but it should always be beneficial to fold this sooner in IR
for all targets.
https://rise4fun.com/Alive/vaiW
Name: sext add nsw
%add = add nsw i8 %i, C0
%ext = sext i8 %add to i32
%r = add i32 %ext, C1
=>
%s = sext i8 %i to i32
%r = add i32 %s, sext(C0)+C1
Name: zext add nuw
%add = add nuw i8 %i, C0
%ext = zext i8 %add to i16
%r = add i16 %ext, C1
=>
%s = zext i8 %i to i16
%r = add i16 %s, zext(C0)+C1
llvm-svn: 355118
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index e2d4774..4b0199d 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -822,6 +822,47 @@
return nullptr;
}
+/// Wrapping flags may allow combining constants separated by an extend.
+static Instruction *foldNoWrapAdd(BinaryOperator &Add,
+ InstCombiner::BuilderTy &Builder) {
+ Value *Op0 = Add.getOperand(0), *Op1 = Add.getOperand(1);
+ Type *Ty = Add.getType();
+ Constant *Op1C;
+ if (!match(Op1, m_Constant(Op1C)))
+ return nullptr;
+
+ // Try this match first because it results in an add in the narrow type.
+ // (zext (X +nuw C2)) + C1 --> zext (X + (C2 + trunc(C1)))
+ Value *X;
+ const APInt *C1, *C2;
+ if (match(Op1, m_APInt(C1)) &&
+ match(Op0, m_OneUse(m_ZExt(m_NUWAdd(m_Value(X), m_APInt(C2))))) &&
+ C1->isNegative() && C1->sge(-C2->sext(C1->getBitWidth()))) {
+ Constant *NewC =
+ ConstantInt::get(X->getType(), *C2 + C1->trunc(C2->getBitWidth()));
+ return new ZExtInst(Builder.CreateNUWAdd(X, NewC), Ty);
+ }
+
+ // More general combining of constants in the wide type.
+ // (sext (X +nsw NarrowC)) + C --> (sext X) + (sext(NarrowC) + C)
+ Constant *NarrowC;
+ if (match(Op0, m_OneUse(m_SExt(m_NSWAdd(m_Value(X), m_Constant(NarrowC)))))) {
+ Constant *WideC = ConstantExpr::getSExt(NarrowC, Ty);
+ Constant *NewC = ConstantExpr::getAdd(WideC, Op1C);
+ Value *WideX = Builder.CreateSExt(X, Ty);
+ return BinaryOperator::CreateAdd(WideX, NewC);
+ }
+ // (zext (X +nuw NarrowC)) + C --> (zext X) + (zext(NarrowC) + C)
+ if (match(Op0, m_OneUse(m_ZExt(m_NUWAdd(m_Value(X), m_Constant(NarrowC)))))) {
+ Constant *WideC = ConstantExpr::getZExt(NarrowC, Ty);
+ Constant *NewC = ConstantExpr::getAdd(WideC, Op1C);
+ Value *WideX = Builder.CreateZExt(X, Ty);
+ return BinaryOperator::CreateAdd(WideX, NewC);
+ }
+
+ return nullptr;
+}
+
Instruction *InstCombiner::foldAddWithConstant(BinaryOperator &Add) {
Value *Op0 = Add.getOperand(0), *Op1 = Add.getOperand(1);
Constant *Op1C;
@@ -870,14 +911,6 @@
C2->isMinSignedValue() && C2->sext(Ty->getScalarSizeInBits()) == *C)
return CastInst::Create(Instruction::SExt, X, Ty);
- // (add (zext (add nuw X, C2)), C) --> (zext (add nuw X, C2 + C))
- if (match(Op0, m_OneUse(m_ZExt(m_NUWAdd(m_Value(X), m_APInt(C2))))) &&
- C->isNegative() && C->sge(-C2->sext(C->getBitWidth()))) {
- Constant *NewC =
- ConstantInt::get(X->getType(), *C2 + C->trunc(C2->getBitWidth()));
- return new ZExtInst(Builder.CreateNUWAdd(X, NewC), Ty);
- }
-
if (C->isOneValue() && Op0->hasOneUse()) {
// add (sext i1 X), 1 --> zext (not X)
// TODO: The smallest IR representation is (select X, 0, 1), and that would
@@ -1050,6 +1083,9 @@
if (Instruction *X = foldAddWithConstant(I))
return X;
+ if (Instruction *X = foldNoWrapAdd(I, Builder))
+ return X;
+
// FIXME: This should be moved into the above helper function to allow these
// transforms for general constant or constant splat vectors.
Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);