From fc375d22001d27ba6d22db67821da057e36f7f89 Mon Sep 17 00:00:00 2001 From: Bob Wilson Date: Thu, 4 Feb 2010 23:32:37 +0000 Subject: [PATCH] Do not reassociate expressions with i1 type. SimplifyCFG converts some short-circuited conditions to AND/OR expressions, and those expressions are often converted back to a short-circuited form in code gen. The original source order may have been optimized to take advantage of the expected values, and if we reassociate them, we change the order and subvert that optimization. Radar 7497329. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@95333 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Transforms/Scalar/Reassociate.cpp | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/lib/Transforms/Scalar/Reassociate.cpp b/lib/Transforms/Scalar/Reassociate.cpp index 4a99f4a844e..1decde13b83 100644 --- a/lib/Transforms/Scalar/Reassociate.cpp +++ b/lib/Transforms/Scalar/Reassociate.cpp @@ -933,6 +933,15 @@ void Reassociate::ReassociateBB(BasicBlock *BB) { isa(BI->getType())) continue; // Floating point ops are not associative. + // Do not reassociate boolean (i1) expressions. We want to preserve the + // original order of evaluation for short-circuited comparisons that + // SimplifyCFG has folded to AND/OR expressions. If the expression + // is not further optimized, it is likely to be transformed back to a + // short-circuited form for code gen, and the source order may have been + // optimized for the most likely conditions. + if (BI->getType()->isInteger(1)) + continue; + // If this is a subtract instruction which is not already in negate form, // see if we can convert it to X+-Y. if (BI->getOpcode() == Instruction::Sub) {