[InstCombine] Handle ssubo always overflow

Following D60483 and D60497, this adds support for AlwaysOverflows
handling for ssubo. This is the last case we can handle right now.

Differential Revision: https://reviews.llvm.org/D60518

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@358100 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/InstCombine/InstCombineCompares.cpp b/lib/Transforms/InstCombine/InstCombineCompares.cpp
index bc99b177a7e2416c1dd675767b48fdd766b23ee0..2c7d70e4db4c1752af0ea76e3bbdaa69dff371d7 100644 (file)
--- a/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -3997,15 +3997,15 @@ bool InstCombiner::OptimizeOverflowCheck(OverflowCheckFlavor OCF, Value *LHS,
       if (OR == OverflowResult::NeverOverflows)
         return SetResult(Builder.CreateNUWSub(LHS, RHS), Builder.getFalse(),
                          true);
-
-      if (OR == OverflowResult::AlwaysOverflows)
-        return SetResult(Builder.CreateSub(LHS, RHS), Builder.getTrue(), true);
     } else {
       OR = computeOverflowForSignedSub(LHS, RHS, &OrigI);
       if (OR == OverflowResult::NeverOverflows)
         return SetResult(Builder.CreateNSWSub(LHS, RHS), Builder.getFalse(),
                          true);
     }
+
+    if (OR == OverflowResult::AlwaysOverflows)
+      return SetResult(Builder.CreateSub(LHS, RHS), Builder.getTrue(), true);
     break;
   }
 

diff --git a/test/Transforms/InstCombine/with_overflow.ll b/test/Transforms/InstCombine/with_overflow.ll
index af9b133349704bf79678f6c100b0530faac299e7..e80da2afe2f6e19053ceb9113bb66fd439dc6a2d 100644 (file)
--- a/test/Transforms/InstCombine/with_overflow.ll
+++ b/test/Transforms/InstCombine/with_overflow.ll
@@ -582,8 +582,9 @@ define { i8, i1 } @ssub_always_overflow(i8 %x) nounwind {
 ; CHECK-LABEL: @ssub_always_overflow(
 ; CHECK-NEXT:    [[C:%.*]] = icmp sgt i8 [[X:%.*]], 29
 ; CHECK-NEXT:    [[Y:%.*]] = select i1 [[C]], i8 [[X]], i8 29
-; CHECK-NEXT:    [[A:%.*]] = call { i8, i1 } @llvm.ssub.with.overflow.i8(i8 -100, i8 [[Y]])
-; CHECK-NEXT:    ret { i8, i1 } [[A]]
+; CHECK-NEXT:    [[A:%.*]] = sub nuw i8 -100, [[Y]]
+; CHECK-NEXT:    [[TMP1:%.*]] = insertvalue { i8, i1 } { i8 undef, i1 true }, i8 [[A]], 0
+; CHECK-NEXT:    ret { i8, i1 } [[TMP1]]
 ;
   %c = icmp sgt i8 %x, 29
   %y = select i1 %c, i8 %x, i8 29