From 0b0803ae1508ff514dd7b471a2a3bcd1e83cb0ef Mon Sep 17 00:00:00 2001 From: Chris Lattner Date: Sun, 17 Feb 2008 20:51:26 +0000 Subject: [PATCH] Split up subtracts into add+negate if they have a reassociable use or operand that is also a subtract. This implements PR2047 and Transforms/Reassociate/subtest2.ll git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@47241 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Transforms/Scalar/Reassociate.cpp | 13 ++++++++----- test/Transforms/Reassociate/subtest2.ll | 13 +++++++++++++ 2 files changed, 21 insertions(+), 5 deletions(-) create mode 100644 test/Transforms/Reassociate/subtest2.ll diff --git a/lib/Transforms/Scalar/Reassociate.cpp b/lib/Transforms/Scalar/Reassociate.cpp index d0537ea8c43..bec91dbe67c 100644 --- a/lib/Transforms/Scalar/Reassociate.cpp +++ b/lib/Transforms/Scalar/Reassociate.cpp @@ -399,13 +399,16 @@ static bool ShouldBreakUpSubtract(Instruction *Sub) { return false; // Don't bother to break this up unless either the LHS is an associable add or - // if this is only used by one. - if (isReassociableOp(Sub->getOperand(0), Instruction::Add)) + // subtract or if this is only used by one. + if (isReassociableOp(Sub->getOperand(0), Instruction::Add) || + isReassociableOp(Sub->getOperand(0), Instruction::Sub)) return true; - if (isReassociableOp(Sub->getOperand(1), Instruction::Add)) + if (isReassociableOp(Sub->getOperand(1), Instruction::Add) || + isReassociableOp(Sub->getOperand(0), Instruction::Sub)) return true; - - if (Sub->hasOneUse() && isReassociableOp(Sub->use_back(), Instruction::Add)) + if (Sub->hasOneUse() && + (isReassociableOp(Sub->use_back(), Instruction::Add) || + isReassociableOp(Sub->use_back(), Instruction::Sub))) return true; return false; diff --git a/test/Transforms/Reassociate/subtest2.ll b/test/Transforms/Reassociate/subtest2.ll new file mode 100644 index 00000000000..c81e9b38def --- /dev/null +++ b/test/Transforms/Reassociate/subtest2.ll @@ -0,0 +1,13 @@ +; With sub reassociation, constant folding can eliminate the uses of %a. +; +; RUN: llvm-as < %s | opt -reassociate -instcombine | llvm-dis | grep %a | count 1 +; PR2047 + +define i32 @test(i32 %a, i32 %b, i32 %c) nounwind { +entry: + %tmp3 = sub i32 %a, %b ; [#uses=1] + %tmp5 = sub i32 %tmp3, %c ; [#uses=1] + %tmp7 = sub i32 %tmp5, %a ; [#uses=1] + ret i32 %tmp7 +} +