From 4052afef7f803222301b9d05f08630f293d81dcc Mon Sep 17 00:00:00 2001 From: Chris Lattner Date: Mon, 11 Jan 2010 04:05:13 +0000 Subject: Extend CanEvaluateZExtd to handle and/or/xor more aggressively in the BitsToClear case. This allows it to promote expressions which have an and/or/xor after the lshr, promoting cases like test2 (from PR4216) and test3 (random extample extracted from a spec benchmark). clang now compiles the code in PR4216 into: _test_bitfield: ## @test_bitfield movl %edi, %eax orl $194, %eax movl $4294902010, %ecx andq %rax, %rcx orl $32768, %edi andq $39936, %rdi movq %rdi, %rax orq %rcx, %rax ret instead of: _test_bitfield: ## @test_bitfield movl %edi, %eax orl $194, %eax movl $4294902010, %ecx andq %rax, %rcx shrl $8, %edi orl $128, %edi shlq $8, %rdi andq $39936, %rdi movq %rdi, %rax orq %rcx, %rax ret which is still not great, but is progress. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@93145 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Transforms/InstCombine/InstCombineCasts.cpp | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) (limited to 'lib/Transforms/InstCombine/InstCombineCasts.cpp') diff --git a/lib/Transforms/InstCombine/InstCombineCasts.cpp b/lib/Transforms/InstCombine/InstCombineCasts.cpp index be0734c..939c2b1 100644 --- a/lib/Transforms/InstCombine/InstCombineCasts.cpp +++ b/lib/Transforms/InstCombine/InstCombineCasts.cpp @@ -634,6 +634,20 @@ static bool CanEvaluateZExtd(Value *V, const Type *Ty, unsigned &BitsToClear) { if (BitsToClear == 0 && Tmp == 0) return true; + // If the operation is an AND/OR/XOR and the bits to clear are zero in the + // other side, BitsToClear is ok. + if (Tmp == 0 && + (Opc == Instruction::And || Opc == Instruction::Or || + Opc == Instruction::Xor)) { + // We use MaskedValueIsZero here for generality, but the case we care + // about the most is constant RHS. + unsigned VSize = V->getType()->getScalarSizeInBits(); + if (MaskedValueIsZero(I->getOperand(1), + APInt::getHighBitsSet(VSize, BitsToClear))) + return true; + } + + // Otherwise, we don't know how to analyze this BitsToClear case yet. return false; case Instruction::LShr: @@ -652,6 +666,8 @@ static bool CanEvaluateZExtd(Value *V, const Type *Ty, unsigned &BitsToClear) { case Instruction::Select: if (!CanEvaluateZExtd(I->getOperand(1), Ty, Tmp) || !CanEvaluateZExtd(I->getOperand(2), Ty, BitsToClear) || + // TODO: If important, we could handle the case when the BitsToClear are + // known zero in the disagreeing side. Tmp != BitsToClear) return false; return true; @@ -665,6 +681,8 @@ static bool CanEvaluateZExtd(Value *V, const Type *Ty, unsigned &BitsToClear) { return false; for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i) if (!CanEvaluateZExtd(PN->getIncomingValue(i), Ty, Tmp) || + // TODO: If important, we could handle the case when the BitsToClear + // are known zero in the disagreeing input. Tmp != BitsToClear) return false; return true; -- cgit v1.1