Instcombine: cast (X != 0) to int, cast (X == 1) to int -> X iff X has only the...

This implements set.ll:test20.

This triggers 2x on povray, 9x on mesa, 11x on gcc, 2x on crafty, 1x on eon,
6x on perlbmk and 11x on m88ksim.

It allows us to compile these two functions into the same code:

struct s { unsigned int bit : 1; };
unsigned foo(struct s *p) {
  if (p->bit)
    return 1;
  else
    return 0;
}
unsigned bar(struct s *p) { return p->bit; }

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@21690 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index 5fe95540de37a4b5ad6d2f4b6fef87de4fb24a2d..fa615cfc5178361bb2027bd7519a2a6a534aa02f 100644 (file)
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -3553,9 +3553,30 @@ Instruction *InstCombiner::visitCastInst(CastInst &CI) {
           return new ShiftInst(Instruction::Shl, Op0c, Op1);
         }
         break;
+      case Instruction::SetNE:
+      case Instruction::SetEQ:
+        // We if we are just checking for a seteq of a single bit and casting it
+        // to an integer.  If so, shift the bit to the appropriate place then
+        // cast to integer to avoid the comparison.
+        if (ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
+          // cast (X != 0) to int, cast (X == 1) to int  -> X iff X has only the
+          // low bit set.
+          bool isSetNE = SrcI->getOpcode() == Instruction::SetNE;
+          if ((isSetNE && Op1C->getRawValue() == 0) ||
+              (!isSetNE && Op1C->getRawValue() == 1)) {
+            Constant *Not1 = 
+              ConstantExpr::getNot(ConstantInt::get(Op0->getType(), 1));
+            if (MaskedValueIsZero(Op0, cast<ConstantIntegral>(Not1))) {
+              if (CI.getType() == Op0->getType())
+                return ReplaceInstUsesWith(CI, Op0);
+              else
+                return new CastInst(Op0, CI.getType());
+            }
+          }
+        }
+        break;
       }
     }
-
   return 0;
 }
 
@@ -4603,8 +4624,9 @@ Instruction *InstCombiner::visitAllocationInst(AllocationInst &AI) {
       // Now that I is pointing to the first non-allocation-inst in the block,
       // insert our getelementptr instruction...
       //
-      std::vector<Value*> Idx(2, Constant::getNullValue(Type::IntTy));
-      Value *V = new GetElementPtrInst(New, Idx, New->getName()+".sub", It);
+      Value *NullIdx = Constant::getNullValue(Type::IntTy);
+      Value *V = new GetElementPtrInst(New, NullIdx, NullIdx,
+                                       New->getName()+".sub", It);
 
       // Now make everything use the getelementptr instead of the original
       // allocation.