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Add support for combining GEPs across PHI nodes

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Currently LLVM will generally merge GEPs. This allows backends to use more
complex addressing modes. In some cases this is not happening because there
is PHI inbetween the two GEPs:

  GEP1--\
        |-->PHI1-->GEP3
  GEP2--/

This patch checks to see if GEP1 and GEP2 are similiar enough that they can be
cloned (GEP12) in GEP3's BB, allowing GEP->GEP merging (GEP123):

  GEP1--\                     --\                           --\
        |-->PHI1-->GEP3  ==>    |-->PHI2->GEP12->GEP3 == >    |-->PHI2->GEP123
  GEP2--/                     --/                           --/

This also breaks certain use chains that are preventing GEP->GEP merges that the
the existing instcombine would merge otherwise.

Tests included.

rdar://15547484

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209049 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Louis Gerbarg
2014-05-16 23:47:24 +00:00
parent 70f8b47a65
commit 2d1fa5f718
2 changed files with 115 additions and 0 deletions
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56
test/Transforms/InstCombine/gepphigep.ll Normal file
View File

@@ -0,0 +1,56 @@
; RUN: opt -instcombine -S < %s | FileCheck %s
%struct1 = type { %struct2*, i32, i32, i32 }
%struct2 = type { i32, i32 }
define i32 @test1(%struct1* %dm, i1 %tmp4, i64 %tmp9, i64 %tmp19) {
bb:
%tmp = getelementptr inbounds %struct1* %dm, i64 0, i32 0
%tmp1 = load %struct2** %tmp, align 8
br i1 %tmp4, label %bb1, label %bb2
bb1:
%tmp10 = getelementptr inbounds %struct2* %tmp1, i64 %tmp9
%tmp11 = getelementptr inbounds %struct2* %tmp10, i64 0, i32 0
store i32 0, i32* %tmp11, align 4
br label %bb3
bb2:
%tmp20 = getelementptr inbounds %struct2* %tmp1, i64 %tmp19
%tmp21 = getelementptr inbounds %struct2* %tmp20, i64 0, i32 0
store i32 0, i32* %tmp21, align 4
br label %bb3
bb3:
%phi = phi %struct2* [ %tmp10, %bb1 ], [ %tmp20, %bb2 ]
%tmp24 = getelementptr inbounds %struct2* %phi, i64 0, i32 1
%tmp25 = load i32* %tmp24, align 4
ret i32 %tmp25
; CHECK-LABEL: @test1(
; CHECK: getelementptr inbounds %struct2* %tmp1, i64 %tmp9, i32 0
; CHECK: getelementptr inbounds %struct2* %tmp1, i64 %tmp19, i32 0
; CHECK: %[[PHI:[0-9A-Za-z]+]] = phi i64 [ %tmp9, %bb1 ], [ %tmp19, %bb2 ]
; CHECK: getelementptr inbounds %struct2* %tmp1, i64 %[[PHI]], i32 1
}
define i32 @test2(%struct1* %dm, i1 %tmp4, i64 %tmp9, i64 %tmp19) {
bb:
%tmp = getelementptr inbounds %struct1* %dm, i64 0, i32 0
%tmp1 = load %struct2** %tmp, align 8
%tmp10 = getelementptr inbounds %struct2* %tmp1, i64 %tmp9
%tmp11 = getelementptr inbounds %struct2* %tmp10, i64 0, i32 0
store i32 0, i32* %tmp11, align 4
%tmp20 = getelementptr inbounds %struct2* %tmp1, i64 %tmp19
%tmp21 = getelementptr inbounds %struct2* %tmp20, i64 0, i32 0
store i32 0, i32* %tmp21, align 4
%tmp24 = getelementptr inbounds %struct2* %tmp10, i64 0, i32 1
%tmp25 = load i32* %tmp24, align 4
ret i32 %tmp25
; CHECK-LABEL: @test2(
; CHECK: getelementptr inbounds %struct2* %tmp1, i64 %tmp9, i32 0
; CHECK: getelementptr inbounds %struct2* %tmp1, i64 %tmp19, i32 0
; CHECK: getelementptr inbounds %struct2* %tmp1, i64 %tmp9, i32 1
}