From 6fdb6b8fd4e18c0741a839a11d7dee7077bc7505 Mon Sep 17 00:00:00 2001 From: David Majnemer Date: Tue, 18 Nov 2014 09:31:41 +0000 Subject: [PATCH] InstCombine: Fold away tautological masked compares It is impossible for (x & INT_MAX) == 0 && x == INT_MAX to ever be true. While this sort of reasoning should normally live in InstSimplify, the machinery that derives this result is not trivial to split out. llvm-svn: 222230 --- .../Transforms/InstCombine/InstCombineAndOrXor.cpp | 2 +- llvm/test/Transforms/InstCombine/icmp-logical.ll | 20 ++++++++++++++++++++ 2 files changed, 21 insertions(+), 1 deletion(-) diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp index 35f0586..55ebced 100644 --- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp +++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp @@ -776,7 +776,7 @@ static Value *foldLogOpOfMaskedICmps(ICmpInst *LHS, ICmpInst *RHS, bool IsAnd, // whole construct if (((BCst->getValue() & DCst->getValue()) & (CCst->getValue() ^ ECst->getValue())) != 0) - return nullptr; + return ConstantInt::get(LHS->getType(), !IsAnd); Value *newOr1 = Builder->CreateOr(B, D); Value *newOr2 = ConstantExpr::getOr(CCst, ECst); Value *newAnd = Builder->CreateAnd(A, newOr1); diff --git a/llvm/test/Transforms/InstCombine/icmp-logical.ll b/llvm/test/Transforms/InstCombine/icmp-logical.ll index d5d8cbc..faae201 100644 --- a/llvm/test/Transforms/InstCombine/icmp-logical.ll +++ b/llvm/test/Transforms/InstCombine/icmp-logical.ll @@ -150,3 +150,23 @@ define i1 @nomask_rhs(i32 %in) { %val = or i1 %tst1, %tst2 ret i1 %val } + +define i1 @fold_mask_cmps_to_false(i32 %x) { +; CHECK-LABEL: @fold_mask_cmps_to_false +; CHECK: ret i1 false + %1 = and i32 %x, 2147483647 + %2 = icmp eq i32 %1, 0 + %3 = icmp eq i32 %x, 2147483647 + %4 = and i1 %3, %2 + ret i1 %4 +} + +define i1 @fold_mask_cmps_to_true(i32 %x) { +; CHECK-LABEL: @fold_mask_cmps_to_true +; CHECK: ret i1 true + %1 = and i32 %x, 2147483647 + %2 = icmp ne i32 %1, 0 + %3 = icmp ne i32 %x, 2147483647 + %4 = or i1 %3, %2 + ret i1 %4 +} -- 2.7.4