[IndVar] Don't widen loop compare unless IV user is sign extended.

PR21030

llvm-svn: 218539

2 files changed, 32 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
index 7cc34e1ad86..68a134ebfd8 100644
--- a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -650,7 +650,7 @@ namespace {
   struct WideIVInfo {
     PHINode *NarrowIV;
     Type *WidestNativeType; // Widest integer type created [sz]ext
-    bool IsSigned;          // Was an sext user seen before a zext?
+    bool IsSigned;          // Was a sext user seen before a zext?
 
     WideIVInfo() : NarrowIV(nullptr), WidestNativeType(nullptr),
                    IsSigned(false) {}
@@ -936,7 +936,11 @@ bool WidenIV::WidenLoopCompare(NarrowIVDefUse DU) {
   if (!Cmp)
     return false;
 
-  bool IsSigned = CmpInst::isSigned(Cmp->getPredicate());
+  // Must be a signed compare.
+  if (!CmpInst::isSigned(Cmp->getPredicate()))
+    return false;
+
+  // Must be a signed IV user.
   if (!IsSigned)
     return false;
 
diff --git a/llvm/test/Transforms/IndVarSimplify/widen-loop-comp.ll b/llvm/test/Transforms/IndVarSimplify/widen-loop-comp.ll
index a6963948d8b..b85fc6d1e4c 100644
--- a/llvm/test/Transforms/IndVarSimplify/widen-loop-comp.ll
+++ b/llvm/test/Transforms/IndVarSimplify/widen-loop-comp.ll
@@ -136,3 +136,29 @@ for.body:
 for.end:
   ret i32 %sum.0
 }
+
+declare i32 @fn1(i8 signext)
+
+; PR21030
+; CHECK-LABEL: @test4
+; CHECK: for.body:
+; CHECK: phi i32
+; CHECK: icmp sgt i8
+
+define i32 @test4(i32 %a) {
+entry:
+  br label %for.body
+
+for.body:
+  %c.07 = phi i8 [ -3, %entry ], [ %dec, %for.body ]
+  %conv6 = zext i8 %c.07 to i32
+  %or = or i32 %a, %conv6
+  %conv3 = trunc i32 %or to i8
+  %call = call i32 @fn1(i8 signext %conv3)
+  %dec = add i8 %c.07, -1
+  %cmp = icmp sgt i8 %dec, -14
+  br i1 %cmp, label %for.body, label %for.end
+
+for.end:
+  ret i32 0
+}