Teach EarlyCSE to do trivial CSE of loads and read-only calls.

On 176.gcc, this catches 13090 loads and calls, and increases the
number of simple instructions CSE'd from 29658 to 36208.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122727 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 45 insertions, 0 deletions

diff --git a/test/Transforms/EarlyCSE/basic.ll b/test/Transforms/EarlyCSE/basic.ll
index 6cfd0a9..a761ef7 100644
--- a/test/Transforms/EarlyCSE/basic.ll
+++ b/test/Transforms/EarlyCSE/basic.ll
@@ -30,3 +30,48 @@ define void @test1(i8 %V, i32 *%P) {
   ; CHECK-NEXT: volatile store i32 %G
   ret void
 }
+
+
+;; Simple load value numbering.
+; CHECK: @test2
+define i32 @test2(i32 *%P) {
+  %V1 = load i32* %P
+  %V2 = load i32* %P
+  %Diff = sub i32 %V1, %V2
+  ret i32 %Diff
+  ; CHECK: ret i32 0
+}
+
+;; Cross block load value numbering.
+; CHECK: @test3
+define i32 @test3(i32 *%P, i1 %Cond) {
+  %V1 = load i32* %P
+  br i1 %Cond, label %T, label %F
+T:
+  store i32 4, i32* %P
+  ret i32 42
+F:
+  %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: @test4
+define i32 @test4(i32 *%P, i1 %Cond) {
+  %V1 = load i32* %P
+  br i1 %Cond, label %T, label %F
+T:
+  ret i32 42
+F:
+  ; Clobbers V1
+  store i32 42, i32* %P
+  
+  %V2 = load i32* %P
+  %Diff = sub i32 %V1, %V2
+  ret i32 %Diff
+  ; CHECK: F:
+  ; CHECK: ret i32 %Diff
+}