implement InstCombine/and-compare.ll:test1. This compiles:

typedef struct { unsigned prefix : 4; unsigned code : 4; unsigned unsigned_p : 4; } tree_common;
int foo(tree_common *a, tree_common *b) { return a->code == b->code; }

into:

_foo:
        movl 4(%esp), %eax
        movl 8(%esp), %ecx
        movl (%eax), %eax
        xorl (%ecx), %eax
        # TRUNCATE movb %al, %al
        shrb $4, %al
        testb %al, %al
        sete %al
        movzbl %al, %eax
        ret

instead of:

_foo:
        movl 8(%esp), %eax
        movb (%eax), %al
        shrb $4, %al
        movl 4(%esp), %ecx
        movb (%ecx), %cl
        shrb $4, %cl
        cmpb %al, %cl
        sete %al
        movzbl %al, %eax
        ret

saving one cycle by eliminating a shift.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@31727 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index f636442bb7fecee68419ee740c617c046f29236d..2e3f9aaa10985c0ab9888e859503a6d0de783754 100644 (file)
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -4950,6 +4950,32 @@ Instruction *InstCombiner::visitSetCondInst(SetCondInst &I) {
       return BinaryOperator::create(I.getOpcode(), B,
                                     Constant::getNullValue(B->getType()));
     }
+    
+    Value *C, *D;
+    // (X&Z) == (Y&Z) -> (X^Y) & Z == 0
+    if (Op0->hasOneUse() && Op1->hasOneUse() &&
+        match(Op0, m_And(m_Value(A), m_Value(B))) && 
+        match(Op1, m_And(m_Value(C), m_Value(D)))) {
+      Value *X = 0, *Y = 0, *Z = 0;
+      
+      if (A == C) {
+        X = B; Y = D; Z = A;
+      } else if (A == D) {
+        X = B; Y = C; Z = A;
+      } else if (B == C) {
+        X = A; Y = D; Z = B;
+      } else if (B == D) {
+        X = A; Y = C; Z = B;
+      }
+      
+      if (X) {   // Build (X^Y) & Z
+        Op1 = InsertNewInstBefore(BinaryOperator::createXor(X, Y, "tmp"), I);
+        Op1 = InsertNewInstBefore(BinaryOperator::createAnd(Op1, Z, "tmp"), I);
+        I.setOperand(0, Op1);
+        I.setOperand(1, Constant::getNullValue(Op1->getType()));
+        return &I;
+      }
+    }
   }
   return Changed ? &I : 0;
 }