From 1e16fa302e2c3f68ea8187e8b782397e0b24cd0f Mon Sep 17 00:00:00 2001
From: Hal Finkel <hfinkel@anl.gov>
Date: Mon, 3 Nov 2014 20:21:32 +0000
Subject: EarlyCSE should ignore calls to @llvm.assume

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.

llvm-svn: 221175
---
 llvm/test/Transforms/EarlyCSE/basic.ll | 36 ++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

(limited to 'llvm/test/Transforms')

diff --git a/llvm/test/Transforms/EarlyCSE/basic.ll b/llvm/test/Transforms/EarlyCSE/basic.ll
index 80704df9852..9f3e474aff9 100644
--- a/llvm/test/Transforms/EarlyCSE/basic.ll
+++ b/llvm/test/Transforms/EarlyCSE/basic.ll
@@ -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) {
-- 
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