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author | Dan Gohman <dan433584@gmail.com> | 2013-01-31 00:01:45 +0000 |
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committer | Dan Gohman <dan433584@gmail.com> | 2013-01-31 00:01:45 +0000 |
commit | d363ae52995059906d99f7588f47bf891e7db485 (patch) | |
tree | 5422d9606820e707f04d8569a5097619f31c86a1 | |
parent | 69f60e7c4a77866b3d0a5907e4955baa05216a20 (diff) | |
download | llvm-d363ae52995059906d99f7588f47bf891e7db485.tar.gz llvm-d363ae52995059906d99f7588f47bf891e7db485.tar.bz2 llvm-d363ae52995059906d99f7588f47bf891e7db485.tar.xz |
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.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173995 91177308-0d34-0410-b5e6-96231b3b80d8
-rw-r--r-- | lib/IR/ConstantFold.cpp | 11 | ||||
-rw-r--r-- | test/Assembler/ConstantExprNoFold.ll | 23 |
2 files changed, 28 insertions, 6 deletions
diff --git a/lib/IR/ConstantFold.cpp b/lib/IR/ConstantFold.cpp index 417e0d14eb..587b7ce88a 100644 --- a/lib/IR/ConstantFold.cpp +++ b/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<GlobalValue>(CE1Op0) && isa<GlobalValue>(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/test/Assembler/ConstantExprNoFold.ll b/test/Assembler/ConstantExprNoFold.ll new file mode 100644 index 0000000000..83e8909b5e --- /dev/null +++ b/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)) |