From 50ca4d37f7f3b460c6441eb5ad14625a7d86b5d9 Mon Sep 17 00:00:00 2001 From: Duncan Sands Date: Thu, 3 Feb 2011 09:37:39 +0000 Subject: [PATCH] Improve threading of comparisons over select instructions (spotted by my auto-simplifier). This has a big impact on Ada code, but not much else. Unfortunately the impact is mostly negative! This is due to PR9004 (aka SCCP failing to resolve conditional branch conditions in the destination blocks of the branch), in which simple correlated expressions are not resolved but complicated ones are, so simplifying has a bad effect! git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@124788 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Analysis/InstructionSimplify.cpp | 28 +++++++++++++-- .../InstSimplify/2011-01-18-Compare.ll | 35 +++++++++++++++++++ 2 files changed, 60 insertions(+), 3 deletions(-) diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp index 4b9b648aa6c..156e7853059 100644 --- a/lib/Analysis/InstructionSimplify.cpp +++ b/lib/Analysis/InstructionSimplify.cpp @@ -395,17 +395,39 @@ static Value *ThreadCmpOverSelect(CmpInst::Predicate Pred, Value *LHS, assert(isa(LHS) && "Not comparing with a select instruction!"); SelectInst *SI = cast(LHS); - // Now that we have "cmp select(cond, TV, FV), RHS", analyse it. + // Now that we have "cmp select(Cond, TV, FV), RHS", analyse it. // Does "cmp TV, RHS" simplify? if (Value *TCmp = SimplifyCmpInst(Pred, SI->getTrueValue(), RHS, TD, DT, - MaxRecurse)) + MaxRecurse)) { // It does! Does "cmp FV, RHS" simplify? if (Value *FCmp = SimplifyCmpInst(Pred, SI->getFalseValue(), RHS, TD, DT, - MaxRecurse)) + MaxRecurse)) { // It does! If they simplified to the same value, then use it as the // result of the original comparison. if (TCmp == FCmp) return TCmp; + Value *Cond = SI->getCondition(); + // If the false value simplified to false, then the result of the compare + // is equal to "Cond && TCmp". This also catches the case when the false + // value simplified to false and the true value to true, returning "Cond". + if (match(FCmp, m_Zero())) + if (Value *V = SimplifyAndInst(Cond, TCmp, TD, DT, MaxRecurse)) + return V; + // If the true value simplified to true, then the result of the compare + // is equal to "Cond || FCmp". + if (match(TCmp, m_One())) + if (Value *V = SimplifyOrInst(Cond, FCmp, TD, DT, MaxRecurse)) + return V; + // Finally, if the false value simplified to true and the true value to + // false, then the result of the compare is equal to "!Cond". + if (match(FCmp, m_One()) && match(TCmp, m_Zero())) + if (Value *V = + SimplifyXorInst(Cond, Constant::getAllOnesValue(Cond->getType()), + TD, DT, MaxRecurse)) + return V; + } + } + return 0; } diff --git a/test/Transforms/InstSimplify/2011-01-18-Compare.ll b/test/Transforms/InstSimplify/2011-01-18-Compare.ll index ed358443d63..e08ee2c6fb5 100644 --- a/test/Transforms/InstSimplify/2011-01-18-Compare.ll +++ b/test/Transforms/InstSimplify/2011-01-18-Compare.ll @@ -132,3 +132,38 @@ define i1 @ashr(i32 %x) { ret i1 %c ; CHECK: ret i1 false } + +define i1 @select1(i1 %cond) { +; CHECK: @select1 + %s = select i1 %cond, i32 1, i32 0 + %c = icmp eq i32 %s, 1 + ret i1 %c +; CHECK: ret i1 %cond +} + +define i1 @select2(i1 %cond) { +; CHECK: @select2 + %x = zext i1 %cond to i32 + %s = select i1 %cond, i32 %x, i32 0 + %c = icmp ne i32 %s, 0 + ret i1 %c +; CHECK: ret i1 %cond +} + +define i1 @select3(i1 %cond) { +; CHECK: @select3 + %x = zext i1 %cond to i32 + %s = select i1 %cond, i32 1, i32 %x + %c = icmp ne i32 %s, 0 + ret i1 %c +; CHECK: ret i1 %cond +} + +define i1 @select4(i1 %cond) { +; CHECK: @select4 + %invert = xor i1 %cond, 1 + %s = select i1 %invert, i32 0, i32 1 + %c = icmp ne i32 %s, 0 + ret i1 %c +; CHECK: ret i1 %cond +} -- 2.34.1