[llvm] r280370 - [InstCombine] remove fold of an icmp pattern that should never happen

[Sanjay Patel via llvm-commits]

Author: spatel
Date: Thu Sep  1 09:20:43 2016
New Revision: 280370

URL: http://llvm.org/viewvc/llvm-project?rev=280370&view=rev
Log:
[InstCombine] remove fold of an icmp pattern that should never happen

While removing a scalar shackle from an icmp fold, I noticed that I couldn't find any tests to trigger
this code path.

The 'and' shrinking transform should be handled by InstCombiner::foldCastedBitwiseLogic()
or eliminated with InstSimplify. The icmp narrowing is part of InstCombiner::foldICmpWithCastAndCast().

Differential Revision: https://reviews.llvm.org/D24031 

Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
    llvm/trunk/test/Transforms/InstCombine/cast.ll

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp?rev=280370&r1=280369&r2=280370&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp Thu Sep  1 09:20:43 2016
@@ -1526,21 +1526,6 @@ Instruction *InstCombiner::foldICmpAndCo
     }
   }
 
-  // If the LHS is an AND of a zext, and we have an equality compare, we can
-  // shrink the and/compare to the smaller type, eliminating the cast.
-  if (ZExtInst *Cast = dyn_cast<ZExtInst>(And->getOperand(0))) {
-    IntegerType *Ty = cast<IntegerType>(Cast->getSrcTy());
-    // Make sure we don't compare the upper bits, SimplifyDemandedBits
-    // should fold the icmp to true/false in that case.
-    if (Cmp.isEquality() && C1->getActiveBits() <= Ty->getBitWidth()) {
-      Value *NewAnd = Builder->CreateAnd(Cast->getOperand(0),
-                                         ConstantExpr::getTrunc(C2, Ty));
-      NewAnd->takeName(And);
-      return new ICmpInst(Cmp.getPredicate(), NewAnd,
-                          ConstantExpr::getTrunc(RHS, Ty));
-    }
-  }
-
   if (Instruction *I = foldICmpAndShift(Cmp, And, C1))
     return I;
 

Modified: llvm/trunk/test/Transforms/InstCombine/cast.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/cast.ll?rev=280370&r1=280369&r2=280370&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/cast.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/cast.ll Thu Sep  1 09:20:43 2016
@@ -371,6 +371,21 @@ define <2 x i1> @test31vec(<2 x i64> %A)
   ret <2 x i1> %D
 }
 
+; Verify that the 'and' was narrowed, the zext was eliminated, and the compare was narrowed
+; even for vectors. Earlier folds should ensure that the icmp(and(zext)) pattern never occurs.
+
+define <2 x i1> @test32vec(<2 x i8> %A) {
+; CHECK-LABEL: @test32vec(
+; CHECK-NEXT:    [[TMP1:%.*]] = and <2 x i8> %A, <i8 42, i8 42>
+; CHECK-NEXT:    [[D:%.*]] = icmp eq <2 x i8> [[TMP1]], <i8 10, i8 10>
+; CHECK-NEXT:    ret <2 x i1> [[D]]
+;
+  %B = zext <2 x i8> %A to <2 x i16>
+  %C = and <2 x i16> %B, <i16 42, i16 42>
+  %D = icmp eq <2 x i16> %C, <i16 10, i16 10>
+  ret <2 x i1> %D
+}
+
 define i32 @test33(i32 %c1) {
 ; CHECK-LABEL: @test33(
 ; CHECK-NEXT:    ret i32 %c1