[llvm] 3b8ae10 - [InstCombine] fix miscompile from umul_with_overflow matching

[Sanjay Patel via llvm-commits]

Author: Sanjay Patel
Date: 2020-07-04T11:16:23-04:00
New Revision: 3b8ae1001f678be00507f15df0ffaccafec1dae9

URL: https://github.com/llvm/llvm-project/commit/3b8ae1001f678be00507f15df0ffaccafec1dae9
DIFF: https://github.com/llvm/llvm-project/commit/3b8ae1001f678be00507f15df0ffaccafec1dae9.diff

LOG: [InstCombine] fix miscompile from umul_with_overflow matching

As noted in PR46561:
https://bugs.llvm.org/show_bug.cgi?id=46561
...it takes something beyond a minimal IR example to trigger
this bug because it relies on matching non-canonical IR.

There are no tests that show the need for matching this
pattern, so I'm just deleting it to fix the miscompile.

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
    llvm/test/Transforms/InstCombine/icmp-mul-zext.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 31cd8e4510fa..f1233b62445d 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -4644,17 +4644,6 @@ static Instruction *processUMulZExtIdiom(ICmpInst &I, Value *MulVal,
   switch (I.getPredicate()) {
   case ICmpInst::ICMP_EQ:
   case ICmpInst::ICMP_NE:
-    // Recognize pattern:
-    //   mulval = mul(zext A, zext B)
-    //   cmp eq/neq mulval, zext trunc mulval
-    if (ZExtInst *Zext = dyn_cast<ZExtInst>(OtherVal))
-      if (Zext->hasOneUse()) {
-        Value *ZextArg = Zext->getOperand(0);
-        if (TruncInst *Trunc = dyn_cast<TruncInst>(ZextArg))
-          if (Trunc->getType()->getPrimitiveSizeInBits() == MulWidth)
-            break; //Recognized
-      }
-
     // Recognize pattern:
     //   mulval = mul(zext A, zext B)
     //   cmp eq/neq mulval, and(mulval, mask), mask selects low MulWidth bits.

diff  --git a/llvm/test/Transforms/InstCombine/icmp-mul-zext.ll b/llvm/test/Transforms/InstCombine/icmp-mul-zext.ll
index 31540e600f9f..9b4d9947d161 100644
--- a/llvm/test/Transforms/InstCombine/icmp-mul-zext.ll
+++ b/llvm/test/Transforms/InstCombine/icmp-mul-zext.ll
@@ -121,16 +121,20 @@ ret2:
   ret i16 %trunc_unnecessary              ; crash visiting this use after corrupting iterator
 }
 
-; FIXME: This miscompiles because of broken pattern matching.
+; This miscompiled because of broken pattern matching.
 
 define i1 @PR46561(i1 %a, i1 %x, i1 %y, i8 %z) {
 ; CHECK-LABEL: @PR46561(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    br i1 [[A:%.*]], label [[COND_TRUE:%.*]], label [[END:%.*]]
 ; CHECK:       cond.true:
+; CHECK-NEXT:    [[MULBOOL:%.*]] = and i1 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    [[TMP0:%.*]] = and i8 [[Z:%.*]], 1
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i8 [[TMP0]], 0
+; CHECK-NEXT:    [[PHI_CMP:%.*]] = xor i1 [[TMP1]], [[MULBOOL]]
 ; CHECK-NEXT:    br label [[END]]
 ; CHECK:       end:
-; CHECK-NEXT:    [[P:%.*]] = phi i1 [ true, [[COND_TRUE]] ], [ false, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    [[P:%.*]] = phi i1 [ [[PHI_CMP]], [[COND_TRUE]] ], [ false, [[ENTRY:%.*]] ]
 ; CHECK-NEXT:    ret i1 [[P]]
 ;
 entry: