From a32038b006c67fb4c9b572133a24050b4c8d40cf Mon Sep 17 00:00:00 2001 From: Chandler Carruth Date: Mon, 20 Oct 2014 10:03:01 +0000 Subject: [PATCH] Fix a miscompile introduced in r220178. The original code had an implicit assumption that if the test for allocas or globals was reached, the two pointers were not equal. With my changes to make the pointer analysis more powerful here, I also had to guard against circumstances where the results weren't useful. That in turn violated the assumption and gave rise to a circumstance in which we could have a store with both the queried pointer and stored pointer rooted at *the same* alloca. Clearly, we cannot ignore such a store. There are other things we might do in this code to better handle the case of both pointers ending up at the same alloca or global, but it seems best to at least make the test explicit in what it intends to check. I've added tests for both the alloca and global case here. llvm-svn: 220190 --- llvm/lib/Analysis/Loads.cpp | 9 +++++---- llvm/test/Transforms/InstCombine/load.ll | 31 +++++++++++++++++++++++++++++++ 2 files changed, 36 insertions(+), 4 deletions(-) diff --git a/llvm/lib/Analysis/Loads.cpp b/llvm/lib/Analysis/Loads.cpp index 65a30f2..bb0d60e 100644 --- a/llvm/lib/Analysis/Loads.cpp +++ b/llvm/lib/Analysis/Loads.cpp @@ -220,11 +220,12 @@ Value *llvm::FindAvailableLoadedValue(Value *Ptr, BasicBlock *ScanBB, return SI->getOperand(0); } - // If Ptr is an alloca and this is a store to a different alloca, ignore - // the store. This is a trivial form of alias analysis that is important - // for reg2mem'd code. + // If both StrippedPtr and StorePtr reach all the way to an alloca or + // global and they are different, ignore the store. This is a trivial form + // of alias analysis that is important for reg2mem'd code. if ((isa(StrippedPtr) || isa(StrippedPtr)) && - (isa(StorePtr) || isa(StorePtr))) + (isa(StorePtr) || isa(StorePtr)) && + StrippedPtr != StorePtr) continue; // If we have alias analysis and it says the store won't modify the loaded diff --git a/llvm/test/Transforms/InstCombine/load.ll b/llvm/test/Transforms/InstCombine/load.ll index 20d40e2..b4b7558 100644 --- a/llvm/test/Transforms/InstCombine/load.ll +++ b/llvm/test/Transforms/InstCombine/load.ll @@ -119,3 +119,34 @@ define <16 x i8> @test13(<2 x i64> %x) { %tmp = load <16 x i8>* bitcast ([4 x i32]* @GLOBAL to <16 x i8>*) ret <16 x i8> %tmp } + +define i8 @test14(i8 %x, i32 %y) { +; This test must not have the store of %x forwarded to the load -- there is an +; intervening store if %y. However, the intervening store occurs with a different +; type and size and to a different pointer value. This is ensuring that none of +; those confuse the analysis into thinking that the second store does not alias +; the first. +; CHECK-LABEL: @test14( +; CHECK: %[[R:.*]] = load i8* +; CHECK-NEXT: ret i8 %[[R]] + %a = alloca i32 + %a.i8 = bitcast i32* %a to i8* + store i8 %x, i8* %a.i8 + store i32 %y, i32* %a + %r = load i8* %a.i8 + ret i8 %r +} + +@test15_global = external global i32 + +define i8 @test15(i8 %x, i32 %y) { +; Same test as @test14 essentially, but using a global instead of an alloca. +; CHECK-LABEL: @test15( +; CHECK: %[[R:.*]] = load i8* +; CHECK-NEXT: ret i8 %[[R]] + %g.i8 = bitcast i32* @test15_global to i8* + store i8 %x, i8* %g.i8 + store i32 %y, i32* @test15_global + %r = load i8* %g.i8 + ret i8 %r +} -- 2.7.4