[InstCombine] don't try to shift an illegal amount (PR26760)

This is the straightforward fix for PR26760:
https://llvm.org/bugs/show_bug.cgi?id=26760

But we still need to make some changes to generalize this helper function
and then send the lshr case into here.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@265960 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 22 insertions, 1 deletions

diff --git a/test/Transforms/InstCombine/shift-shift.ll b/test/Transforms/InstCombine/shift-shift.ll
index 23a45e0967f..2968a9bf3c6 100644
--- a/test/Transforms/InstCombine/shift-shift.ll
+++ b/test/Transforms/InstCombine/shift-shift.ll
@@ -1,7 +1,9 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt < %s -instcombine -S | FileCheck %s
 
-; This would crash if we didn't check for a negative shift.
+; These would crash if we didn't check for a negative shift.
+
+; https://llvm.org/bugs/show_bug.cgi?id=12967
 
 define void @pr12967() {
 ; CHECK-LABEL: @pr12967(
@@ -20,3 +22,22 @@ loop:
   br label %loop
 }
 
+; https://llvm.org/bugs/show_bug.cgi?id=26760
+
+define void @pr26760() {
+; CHECK-LABEL: @pr26760(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label %loop
+; CHECK:       loop:
+; CHECK-NEXT:    br label %loop
+;
+entry:
+  br label %loop
+
+loop:
+  %c = phi i32 [ %shl, %loop ], [ undef, %entry ]
+  %shr = lshr i32 %c, 7
+  %shl = shl i32 %shr, -2
+  br label %loop
+}
+