[llvm] r373167 - [DivRemPairs] Don't assert that we won't ever get expanded-form rem pairs in different BB's (PR43500)

[Roman Lebedev via llvm-commits]

Author: lebedevri
Date: Sun Sep 29 08:25:24 2019
New Revision: 373167

URL: http://llvm.org/viewvc/llvm-project?rev=373167&view=rev
Log:
[DivRemPairs] Don't assert that we won't ever get expanded-form rem pairs in different BB's (PR43500)

If we happen to have the same div in two basic blocks,
and in one of those we also happen to have the rem part,
we'd match the div-rem pair, but the wrong ones.
So let's drop overly-ambiguous assert.

Fixes https://bugs.llvm.org/show_bug.cgi?id=43500

Modified:
    llvm/trunk/lib/Transforms/Scalar/DivRemPairs.cpp
    llvm/trunk/test/Transforms/DivRemPairs/X86/div-expanded-rem-pair.ll

Modified: llvm/trunk/lib/Transforms/Scalar/DivRemPairs.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/DivRemPairs.cpp?rev=373167&r1=373166&r2=373167&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/DivRemPairs.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/DivRemPairs.cpp Sun Sep 29 08:25:24 2019
@@ -233,8 +233,6 @@ static bool optimizeDivRem(Function &F,
     if (!DivDominates && !DT.dominates(RemInst, DivInst)) {
       // We have matching div-rem pair, but they are in two different blocks,
       // neither of which dominates one another.
-      assert(!RemOriginallyWasInExpandedForm &&
-             "Won't happen for expanded-form rem.");
       // FIXME: We could hoist both ops to the common predecessor block?
       continue;
     }

Modified: llvm/trunk/test/Transforms/DivRemPairs/X86/div-expanded-rem-pair.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/DivRemPairs/X86/div-expanded-rem-pair.ll?rev=373167&r1=373166&r2=373167&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/DivRemPairs/X86/div-expanded-rem-pair.ll (original)
+++ llvm/trunk/test/Transforms/DivRemPairs/X86/div-expanded-rem-pair.ll Sun Sep 29 08:25:24 2019
@@ -168,3 +168,39 @@ end:
   %ret = phi i128 [ %rem, %if ], [ 3, %entry ]
   ret i128 %ret
 }
+
+; Even in expanded form, we can end up with div and rem in different basic
+; blocks neither of which dominates each another.
+define i32 @can_have_divrem_in_mutually_nondominating_bbs(i1 %cmp, i32 %a, i32 %b) {
+; CHECK-LABEL: @can_have_divrem_in_mutually_nondominating_bbs(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br i1 [[CMP:%.*]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK:       if.then:
+; CHECK-NEXT:    [[T0:%.*]] = udiv i32 [[A:%.*]], [[B:%.*]]
+; CHECK-NEXT:    [[T1:%.*]] = mul nuw i32 [[T0]], [[B]]
+; CHECK-NEXT:    [[T2_RECOMPOSED:%.*]] = urem i32 [[A]], [[B]]
+; CHECK-NEXT:    br label [[END:%.*]]
+; CHECK:       if.else:
+; CHECK-NEXT:    [[T3:%.*]] = udiv i32 [[A]], [[B]]
+; CHECK-NEXT:    br label [[END]]
+; CHECK:       end:
+; CHECK-NEXT:    [[RET:%.*]] = phi i32 [ [[T2_RECOMPOSED]], [[IF_THEN]] ], [ [[T3]], [[IF_ELSE]] ]
+; CHECK-NEXT:    ret i32 [[RET]]
+;
+entry:
+  br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+  %t0 = udiv i32 %a, %b
+  %t1 = mul nuw i32 %t0, %b
+  %t2 = sub i32 %a, %t1
+  br label %end
+
+if.else:
+  %t3 = udiv i32 %a, %b
+  br label %end
+
+end:
+  %ret = phi i32 [ %t2, %if.then ], [ %t3, %if.else ]
+  ret i32 %ret
+}