diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp --- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp +++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp @@ -185,6 +185,9 @@ return nullptr; } +static Value *takeLog2(IRBuilderBase &Builder, Value *Op, unsigned Depth, + bool DoFold); + Instruction *InstCombinerImpl::visitMul(BinaryOperator &I) { Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1); if (Value *V = @@ -471,6 +474,20 @@ if (Instruction *Ext = narrowMathIfNoOverflow(I)) return Ext; + // (mul Op0 Op1): + // if Log2(Op0) folds away -> + // (shl Op1, Log2(Op0)) + // if Log2(Op1) folds away -> + // (shl Op0, Log2(Op1)) + if (takeLog2(Builder, Op0, /*Depth*/ 0, /*DoFold*/ false)) { + Value *Res = takeLog2(Builder, Op0, /*Depth*/ 0, /*DoFold*/ true); + return replaceInstUsesWith(I, Builder.CreateShl(Op1, Res, I.getName())); + } + if (takeLog2(Builder, Op1, /*Depth*/ 0, /*DoFold*/ false)) { + Value *Res = takeLog2(Builder, Op1, /*Depth*/ 0, /*DoFold*/ true); + return replaceInstUsesWith(I, Builder.CreateShl(Op0, Res, I.getName())); + } + bool Changed = false; if (!HasNSW && willNotOverflowSignedMul(Op0, Op1, I)) { Changed = true; diff --git a/llvm/test/Transforms/InstCombine/mul-pow2.ll b/llvm/test/Transforms/InstCombine/mul-pow2.ll --- a/llvm/test/Transforms/InstCombine/mul-pow2.ll +++ b/llvm/test/Transforms/InstCombine/mul-pow2.ll @@ -3,9 +3,9 @@ declare void @use_i8(i8) define i8 @mul_selectp2_x(i8 %x, i1 %c) { ; CHECK-LABEL: @mul_selectp2_x( -; CHECK-NEXT: [[S:%.*]] = select i1 [[C:%.*]], i8 2, i8 4 -; CHECK-NEXT: [[R:%.*]] = mul i8 [[S]], [[X:%.*]] -; CHECK-NEXT: ret i8 [[R]] +; CHECK-NEXT: [[TMP1:%.*]] = select i1 [[C:%.*]], i8 1, i8 2 +; CHECK-NEXT: [[R1:%.*]] = shl i8 [[X:%.*]], [[TMP1]] +; CHECK-NEXT: ret i8 [[R1]] ; %s = select i1 %c, i8 2, i8 4 %r = mul i8 %s, %x @@ -15,9 +15,10 @@ define i8 @mul_selectp2_x_multiuse_fixme(i8 %x, i1 %c) { ; CHECK-LABEL: @mul_selectp2_x_multiuse_fixme( ; CHECK-NEXT: [[S:%.*]] = select i1 [[C:%.*]], i8 2, i8 4 -; CHECK-NEXT: [[R:%.*]] = mul i8 [[S]], [[X:%.*]] +; CHECK-NEXT: [[TMP1:%.*]] = select i1 [[C]], i8 1, i8 2 +; CHECK-NEXT: [[R1:%.*]] = shl i8 [[X:%.*]], [[TMP1]] ; CHECK-NEXT: call void @use_i8(i8 [[S]]) -; CHECK-NEXT: ret i8 [[R]] +; CHECK-NEXT: ret i8 [[R1]] ; %s = select i1 %c, i8 2, i8 4 %r = mul i8 %s, %x @@ -27,10 +28,9 @@ define i8 @mul_selectp2_x_non_const(i8 %x, i1 %c, i8 %yy) { ; CHECK-LABEL: @mul_selectp2_x_non_const( -; CHECK-NEXT: [[Y:%.*]] = shl nuw i8 1, [[YY:%.*]] -; CHECK-NEXT: [[S:%.*]] = select i1 [[C:%.*]], i8 2, i8 [[Y]] -; CHECK-NEXT: [[R:%.*]] = mul i8 [[S]], [[X:%.*]] -; CHECK-NEXT: ret i8 [[R]] +; CHECK-NEXT: [[TMP1:%.*]] = select i1 [[C:%.*]], i8 1, i8 [[YY:%.*]] +; CHECK-NEXT: [[R1:%.*]] = shl i8 [[X:%.*]], [[TMP1]] +; CHECK-NEXT: ret i8 [[R1]] ; %y = shl i8 1, %yy %s = select i1 %c, i8 2, i8 %y @@ -41,10 +41,10 @@ define i8 @mul_selectp2_x_non_const_multiuse(i8 %x, i1 %c, i8 %yy) { ; CHECK-LABEL: @mul_selectp2_x_non_const_multiuse( ; CHECK-NEXT: [[Y:%.*]] = shl nuw i8 1, [[YY:%.*]] -; CHECK-NEXT: [[S:%.*]] = select i1 [[C:%.*]], i8 2, i8 [[Y]] -; CHECK-NEXT: [[R:%.*]] = mul i8 [[S]], [[X:%.*]] +; CHECK-NEXT: [[TMP1:%.*]] = select i1 [[C:%.*]], i8 1, i8 [[YY]] +; CHECK-NEXT: [[R1:%.*]] = shl i8 [[X:%.*]], [[TMP1]] ; CHECK-NEXT: call void @use_i8(i8 [[Y]]) -; CHECK-NEXT: ret i8 [[R]] +; CHECK-NEXT: ret i8 [[R1]] ; %y = shl i8 1, %yy %s = select i1 %c, i8 2, i8 %y @@ -56,9 +56,9 @@ define i8 @mul_x_selectp2(i8 %xx, i1 %c) { ; CHECK-LABEL: @mul_x_selectp2( ; CHECK-NEXT: [[X:%.*]] = mul i8 [[XX:%.*]], [[XX]] -; CHECK-NEXT: [[S:%.*]] = select i1 [[C:%.*]], i8 8, i8 1 -; CHECK-NEXT: [[R:%.*]] = mul i8 [[X]], [[S]] -; CHECK-NEXT: ret i8 [[R]] +; CHECK-NEXT: [[TMP1:%.*]] = select i1 [[C:%.*]], i8 3, i8 0 +; CHECK-NEXT: [[R1:%.*]] = shl i8 [[X]], [[TMP1]] +; CHECK-NEXT: ret i8 [[R1]] ; %x = mul i8 %xx, %xx %s = select i1 %c, i8 8, i8 1 @@ -80,9 +80,9 @@ define <2 x i8> @mul_x_selectp2_vec(<2 x i8> %xx, i1 %c) { ; CHECK-LABEL: @mul_x_selectp2_vec( ; CHECK-NEXT: [[X:%.*]] = mul <2 x i8> [[XX:%.*]], [[XX]] -; CHECK-NEXT: [[S:%.*]] = select i1 [[C:%.*]], <2 x i8> , <2 x i8> -; CHECK-NEXT: [[R:%.*]] = mul <2 x i8> [[X]], [[S]] -; CHECK-NEXT: ret <2 x i8> [[R]] +; CHECK-NEXT: [[TMP1:%.*]] = select i1 [[C:%.*]], <2 x i8> , <2 x i8> +; CHECK-NEXT: [[R1:%.*]] = shl <2 x i8> [[X]], [[TMP1]] +; CHECK-NEXT: ret <2 x i8> [[R1]] ; %x = mul <2 x i8> %xx, %xx %s = select i1 %c, <2 x i8> , <2 x i8>