Add a missed SCEV fold that is required to continue analyzing the IR produced

by indvars through the scev expander.

trunc(add x, y) --> add(trunc x, y). Currently SCEV largely folds the other way
which is probably wrong, but preserved to minimize churn. Instcombine doesn't
do this fold either, demonstrating a missed optz'n opportunity on code doing
add+trunc+add.

llvm-svn: 123838

1 files changed, 9 insertions, 1 deletions

diff --git a/llvm/test/Analysis/ScalarEvolution/fold.ll b/llvm/test/Analysis/ScalarEvolution/fold.ll
index 202ddd4169a..f46c691f46f 100644
--- a/llvm/test/Analysis/ScalarEvolution/fold.ll
+++ b/llvm/test/Analysis/ScalarEvolution/fold.ll
@@ -1,8 +1,16 @@
 ; RUN: opt -analyze -scalar-evolution %s -S | FileCheck %s
 
-define i16 @test(i8 %x) {
+define i16 @test1(i8 %x) {
   %A = zext i8 %x to i12
   %B = sext i12 %A to i16
 ; CHECK: zext i8 %x to i16
   ret i16 %B
 }
+
+define i8 @test2(i8 %x) {
+  %A = zext i8 %x to i16
+  %B = add i16 %A, 1025
+  %C = trunc i16 %B to i8
+; CHECK: (1 + %x)
+  ret i8 %C
+}