From 6a61fccb96a693fef6f4e88cf597d403c3ccc8a4 Mon Sep 17 00:00:00 2001 From: Dan Gohman Date: Thu, 31 Jan 2013 00:01:45 +0000 Subject: [PATCH] Fix ConstantFold's folding of icmp instructions to recognize that, for example, a one-past-the-end pointer from one global variable may be equal to the base pointer of another global variable. llvm-svn: 173995 --- llvm/lib/IR/ConstantFold.cpp | 11 +++++------ llvm/test/Assembler/ConstantExprNoFold.ll | 23 +++++++++++++++++++++++ 2 files changed, 28 insertions(+), 6 deletions(-) create mode 100644 llvm/test/Assembler/ConstantExprNoFold.ll diff --git a/llvm/lib/IR/ConstantFold.cpp b/llvm/lib/IR/ConstantFold.cpp index 417e0d1..587b7ce8 100644 --- a/llvm/lib/IR/ConstantFold.cpp +++ b/llvm/lib/IR/ConstantFold.cpp @@ -1495,9 +1495,8 @@ static ICmpInst::Predicate evaluateICmpRelation(Constant *V1, Constant *V2, "Surprising getelementptr!"); return isSigned ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT; } else { - // If they are different globals, we don't know what the value is, - // but they can't be equal. - return ICmpInst::ICMP_NE; + // If they are different globals, we don't know what the value is. + return ICmpInst::BAD_ICMP_PREDICATE; } } } else { @@ -1510,10 +1509,10 @@ static ICmpInst::Predicate evaluateICmpRelation(Constant *V1, Constant *V2, default: break; case Instruction::GetElementPtr: // By far the most common case to handle is when the base pointers are - // obviously to the same or different globals. + // obviously to the same global. if (isa(CE1Op0) && isa(CE2Op0)) { - if (CE1Op0 != CE2Op0) // Don't know relative ordering, but not equal - return ICmpInst::ICMP_NE; + if (CE1Op0 != CE2Op0) // Don't know relative ordering. + return ICmpInst::BAD_ICMP_PREDICATE; // Ok, we know that both getelementptr instructions are based on the // same global. From this, we can precisely determine the relative // ordering of the resultant pointers. diff --git a/llvm/test/Assembler/ConstantExprNoFold.ll b/llvm/test/Assembler/ConstantExprNoFold.ll new file mode 100644 index 0000000..83e8909 --- /dev/null +++ b/llvm/test/Assembler/ConstantExprNoFold.ll @@ -0,0 +1,23 @@ +; This test checks to make sure that constant exprs don't fold in some simple +; situations + +; RUN: llvm-as < %s | llvm-dis | FileCheck %s + +; Even give it a datalayout, to tempt folding as much as possible. +target datalayout = "p:32:32" + +@A = global i64 0 +@B = global i64 0 + +; Don't fold this. @A might really be allocated next to @B, in which case the +; icmp should return true. It's not valid to *dereference* in @B from a pointer +; based on @A, but icmp isn't a dereference. + +; CHECK: @C = global i1 icmp eq (i64* getelementptr inbounds (i64* @A, i64 1), i64* @B) +@C = global i1 icmp eq (i64* getelementptr inbounds (i64* @A, i64 1), i64* @B) + +; Don't fold this completely away either. In theory this could be simplified +; to only use a gep on one side of the icmp though. + +; CHECK: @D = global i1 icmp eq (i64* getelementptr inbounds (i64* @A, i64 1), i64* getelementptr inbounds (i64* @B, i64 2)) +@D = global i1 icmp eq (i64* getelementptr inbounds (i64* @A, i64 1), i64* getelementptr inbounds (i64* @B, i64 2)) -- 2.7.4