diff options
| -rw-r--r-- | llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp | 16 | ||||
| -rw-r--r-- | llvm/test/Transforms/InstCombine/abs-1.ll | 27 |
2 files changed, 43 insertions, 0 deletions
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp index 0df56bd0c07..1e4c38c4c84 100644 --- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp +++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp @@ -1628,6 +1628,22 @@ Instruction *InstCombiner::visitSub(BinaryOperator &I) { Value *ShAmtOp = cast<Instruction>(Op1)->getOperand(1); return BinaryOperator::CreateLShr(X, ShAmtOp); } + + if (Op1->hasOneUse()) { + Value *LHS, *RHS; + SelectPatternFlavor SPF = matchSelectPattern(Op1, LHS, RHS).Flavor; + if (SPF == SPF_ABS || SPF == SPF_NABS) { + // This is a negate of an ABS/NABS pattern. Just swap the operands + // of the select. + SelectInst *SI = cast<SelectInst>(Op1); + Value *TrueVal = SI->getTrueValue(); + Value *FalseVal = SI->getFalseValue(); + SI->setTrueValue(FalseVal); + SI->setFalseValue(TrueVal); + // Don't swap prof metadata, we didn't change the branch behavior. + return replaceInstUsesWith(I, SI); + } + } } // Turn this into a xor if LHS is 2^n-1 and the remaining bits are known diff --git a/llvm/test/Transforms/InstCombine/abs-1.ll b/llvm/test/Transforms/InstCombine/abs-1.ll index ab1813c9043..2a94001b69d 100644 --- a/llvm/test/Transforms/InstCombine/abs-1.ll +++ b/llvm/test/Transforms/InstCombine/abs-1.ll @@ -266,3 +266,30 @@ define i8 @shifty_abs_too_many_uses(i8 %x) { ret i8 %abs } +define i8 @negate_abs(i8 %x) { +; CHECK-LABEL: @negate_abs( +; CHECK-NEXT: [[N:%.*]] = sub i8 0, [[X:%.*]] +; CHECK-NEXT: [[C:%.*]] = icmp slt i8 [[X]], 0 +; CHECK-NEXT: [[S:%.*]] = select i1 [[C]], i8 [[X]], i8 [[N]] +; CHECK-NEXT: ret i8 [[S]] +; + %n = sub i8 0, %x + %c = icmp slt i8 %x, 0 + %s = select i1 %c, i8 %n, i8 %x + %r = sub i8 0, %s + ret i8 %r +} + +define <2 x i8> @negate_nabs(<2 x i8> %x) { +; CHECK-LABEL: @negate_nabs( +; CHECK-NEXT: [[N:%.*]] = sub <2 x i8> zeroinitializer, [[X:%.*]] +; CHECK-NEXT: [[C:%.*]] = icmp slt <2 x i8> [[X]], zeroinitializer +; CHECK-NEXT: [[S:%.*]] = select <2 x i1> [[C]], <2 x i8> [[N]], <2 x i8> [[X]] +; CHECK-NEXT: ret <2 x i8> [[S]] +; + %n = sub <2 x i8> zeroinitializer, %x + %c = icmp slt <2 x i8> %x, zeroinitializer + %s = select <2 x i1> %c, <2 x i8> %x, <2 x i8> %n + %r = sub <2 x i8> zeroinitializer, %s + ret <2 x i8> %r +} |
