From a252138942d8d48eb31234e0da09d3d97cb6abad Mon Sep 17 00:00:00 2001
From: David Majnemer <david.majnemer@gmail.com>
Date: Mon, 13 Oct 2014 21:48:30 +0000
Subject: InstCombine: Don't miscompile (x lshr C1) udiv C2

We have a transform that changes:
  (x lshr C1) udiv C2
into:
  x udiv (C2 << C1)

However, it is unsafe to do so if C2 << C1 discards any of C2's bits.

This fixes PR21255.

llvm-svn: 219634
---
 llvm/test/Transforms/InstCombine/div.ll | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

(limited to 'llvm/test/Transforms')

diff --git a/llvm/test/Transforms/InstCombine/div.ll b/llvm/test/Transforms/InstCombine/div.ll
index 5a884ac671d..f2a70fd0f0d 100644
--- a/llvm/test/Transforms/InstCombine/div.ll
+++ b/llvm/test/Transforms/InstCombine/div.ll
@@ -132,11 +132,11 @@ define i32 @test15(i32 %a, i32 %b) nounwind {
 }
 
 define <2 x i64> @test16(<2 x i64> %x) nounwind {
-  %shr = lshr <2 x i64> %x, <i64 3, i64 5>
-  %div = udiv <2 x i64> %shr, <i64 4, i64 6>
+  %shr = lshr <2 x i64> %x, <i64 5, i64 5>
+  %div = udiv <2 x i64> %shr, <i64 6, i64 6>
   ret <2 x i64> %div
 ; CHECK-LABEL: @test16(
-; CHECK-NEXT: udiv <2 x i64> %x, <i64 32, i64 192>
+; CHECK-NEXT: udiv <2 x i64> %x, <i64 192, i64 192>
 ; CHECK-NEXT: ret <2 x i64>
 }
 
@@ -264,3 +264,13 @@ define i32 @test30(i32 %a) {
 ; CHECK-LABEL: @test30(
 ; CHECK-NEXT: ret i32 %a
 }
+
+define <2 x i32> @test31(<2 x i32> %x) nounwind {
+  %shr = lshr <2 x i32> %x, <i32 31, i32 31>
+  %div = udiv <2 x i32> %shr, <i32 2147483647, i32 2147483647>
+  ret <2 x i32> %div
+; CHECK-LABEL: @test31(
+; CHECK-NEXT: %[[shr:.*]] = lshr <2 x i32> %x, <i32 31, i32 31>
+; CHECK-NEXT: udiv <2 x i32> %[[shr]], <i32 2147483647, i32 2147483647>
+; CHECK-NEXT: ret <2 x i32>
+}
-- 
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