Peer through sext/zext when looking for not(cmp).

llvm-svn: 51819

llvm/lib/Target/README.txt

@@ -775,32 +775,6 @@ be done safely if "b" isn't modified between the strlen and memcpy of course.
 
 //===---------------------------------------------------------------------===//
 
-define i32 @test2(float %X, float %Y) {
-entry:
-        %tmp3 = fcmp uno float %X, %Y           ; <i1> [#uses=1]
-        %tmp34 = zext i1 %tmp3 to i8            ; <i8> [#uses=1]
-        %tmp = xor i8 %tmp34, 1         ; <i8> [#uses=1]
-        %toBoolnot5 = zext i8 %tmp to i32               ; <i32> [#uses=1]
-        ret i32 %toBoolnot5
-}
-
-could be optimized further. Instcombine should use its bitwise analysis to
-collapse the zext/xor/zext structure to an xor/zext and then remove the 
-xor by reversing the fcmp.
-
-Desired output:
-
-define i32 @test2(float %X, float %Y) {
-entry:
-        %tmp3 = fcmp ord float %X, %Y           ; <i1> [#uses=1]
-        %tmp34 = zext i1 %tmp3 to i32           ; <i32> [#uses=1]
-        ret i32 %tmp34
-}
-
-To fix this, we need to make CanEvaluateInDifferentType smarter.
-
-//===---------------------------------------------------------------------===//
-
 We should be able to evaluate this loop:
 
 int test(int x_offs) {

llvm/lib/Transforms/Scalar/InstructionCombining.cpp

@@ -5013,6 +5013,25 @@ Instruction *InstCombiner::visitXor(BinaryOperator &I) {
                             FCI->getOperand(0), FCI->getOperand(1));
     }
 
+    // fold (xor(zext(cmp)), 1) and (xor(sext(cmp)), -1) to ext(!cmp).
+    if (CastInst *Op0C = dyn_cast<CastInst>(Op0)) {
+      if (CmpInst *CI = dyn_cast<CmpInst>(Op0C->getOperand(0))) {
+        if (CI->hasOneUse() && Op0C->hasOneUse()) {
+          Instruction::CastOps Opcode = Op0C->getOpcode();
+          if (Opcode == Instruction::ZExt || Opcode == Instruction::SExt) {
+            if (RHS == ConstantExpr::getCast(Opcode, ConstantInt::getTrue(),
+                                             Op0C->getDestTy())) {
+              Instruction *NewCI = InsertNewInstBefore(CmpInst::Create(
+                                     CI->getOpcode(), CI->getInversePredicate(),
+                                     CI->getOperand(0), CI->getOperand(1)), I);
+              NewCI->takeName(CI);
+              return CastInst::Create(Opcode, NewCI, Op0C->getType());
+            }
+          }
+        }
+      }
+    }
+
     if (BinaryOperator *Op0I = dyn_cast<BinaryOperator>(Op0)) {
       // ~(c-X) == X-c-1 == X+(-c-1)
       if (Op0I->getOpcode() == Instruction::Sub && RHS->isAllOnesValue())
@@ -5206,6 +5225,7 @@ Instruction *InstCombiner::visitXor(BinaryOperator &I) {
         }
       }
   }
+
   return Changed ? &I : 0;
 }
 

llvm/test/Transforms/InstCombine/zext-fold.ll

@@ -1,6 +1,5 @@
 ; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep {zext } | count 1
 ; PR1570
-; XFAIL: *
 
 define i32 @test2(float %X, float %Y) {
 entry: