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EarlyCSE should ignore calls to @llvm.assume

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EarlyCSE uses a simple generation scheme for handling memory-based
dependencies, and calls to @llvm.assume (which are marked as writing to memory
to ensure the preservation of control dependencies) disturb that scheme
unnecessarily. Skipping calls to @llvm.assume is legal, and the alternative
(adding AA calls in EarlyCSE) is likely undesirable (we have GVN for that).

Fixes PR21448.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221175 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Hal Finkel
2014-11-03 20:21:32 +00:00
parent fbd383c93c
commit f16d6b1ff1
2 changed files with 48 additions and 0 deletions
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36
test/Transforms/EarlyCSE/basic.ll
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@@ -1,5 +1,6 @@
; RUN: opt < %s -S -early-cse | FileCheck %s
declare void @llvm.assume(i1) nounwind
; CHECK-LABEL: @test1(
define void @test1(i8 %V, i32 *%P) {
@@ -42,6 +43,16 @@ define i32 @test2(i32 *%P) {
; CHECK: ret i32 0
}
; CHECK-LABEL: @test2a(
define i32 @test2a(i32 *%P, i1 %b) {
%V1 = load i32* %P
tail call void @llvm.assume(i1 %b)
%V2 = load i32* %P
%Diff = sub i32 %V1, %V2
ret i32 %Diff
; CHECK: ret i32 0
}
;; Cross block load value numbering.
; CHECK-LABEL: @test3(
define i32 @test3(i32 *%P, i1 %Cond) {
@@ -58,6 +69,22 @@ F:
; CHECK: ret i32 0
}
; CHECK-LABEL: @test3a(
define i32 @test3a(i32 *%P, i1 %Cond, i1 %b) {
%V1 = load i32* %P
br i1 %Cond, label %T, label %F
T:
store i32 4, i32* %P
ret i32 42
F:
tail call void @llvm.assume(i1 %b)
%V2 = load i32* %P
%Diff = sub i32 %V1, %V2
ret i32 %Diff
; CHECK: F:
; CHECK: ret i32 0
}
;; Cross block load value numbering stops when stores happen.
; CHECK-LABEL: @test4(
define i32 @test4(i32 *%P, i1 %Cond) {
@@ -97,6 +124,15 @@ define i32 @test6(i32 *%P) {
; CHECK: ret i32 42
}
; CHECK-LABEL: @test6a(
define i32 @test6a(i32 *%P, i1 %b) {
store i32 42, i32* %P
tail call void @llvm.assume(i1 %b)
%V1 = load i32* %P
ret i32 %V1
; CHECK: ret i32 42
}
;; Trivial dead store elimination.
; CHECK-LABEL: @test7(
define void @test7(i32 *%P) {