From 198e97c4238079f6af0ffd675c2339dcc46b9d8e Mon Sep 17 00:00:00 2001 From: Jin-Gu Kang Date: Sun, 13 Mar 2011 14:05:51 +0000 Subject: [PATCH] Add comment as following: load and store reference same memory location, the memory location is represented by getelementptr with two uses (load and store) and the getelementptr's base is alloca with single use. At this point, instructions from alloca to store can be removed. (this pattern is generated when bitfield is accessed.) For example, %u = alloca %struct.test, align 4 ; [#uses=1] %0 = getelementptr inbounds %struct.test* %u, i32 0, i32 0;[#uses=2] %1 = load i8* %0, align 4 ; [#uses=1] %2 = and i8 %1, -16 ; [#uses=1] %3 = or i8 %2, 5 ; [#uses=1] store i8 %3, i8* %0, align 4 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@127565 91177308-0d34-0410-b5e6-96231b3b80d8 --- .../InstCombine/InstCombineLoadStoreAlloca.cpp | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp index f233ca6af1d..e5ff00fc1dc 100644 --- a/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp +++ b/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp @@ -433,6 +433,18 @@ Instruction *InstCombiner::visitStoreInst(StoreInst &SI) { !SI.isVolatile()) { if (LI == Val) return EraseInstFromFunction(SI); + // load and store reference same memory location, the memory location + // is represented by getelementptr with two uses (load and store) and + // the getelementptr's base is alloca with single use. At this point, + // instructions from alloca to store can be removed. + // (this pattern is generated when bitfield is accessed.) + // For example, + // %u = alloca %struct.test, align 4 ; [#uses=1] + // %0 = getelementptr inbounds %struct.test* %u, i32 0, i32 0;[#uses=2] + // %1 = load i8* %0, align 4 ; [#uses=1] + // %2 = and i8 %1, -16 ; [#uses=1] + // %3 = or i8 %2, 5 ; [#uses=1] + // store i8 %3, i8* %0, align 4 if (Ptr->hasNUses(2)) { if (GetElementPtrInst *GEP = dyn_cast(Ptr)) { if (isa(GEP->getOperand(0))) { -- 2.34.1