When the least bit of C is greater than V, (x&C) must be greater than V
if it is not zero, so the comparison can be simplified.
Although this was suggested in Target/X86/README.txt, it benefits any
architecture with a directly testable form of AND.
Patch by Kevin Schoedel
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@170576
91177308-0d34-0410-b5e6-
96231b3b80d8
Core 2, and "Generic"
//===---------------------------------------------------------------------===//
-
-Testcase:
-int a(int x) { return (x & 127) > 31; }
-
-Current output:
- movl 4(%esp), %eax
- andl $127, %eax
- cmpl $31, %eax
- seta %al
- movzbl %al, %eax
- ret
-
-Ideal output:
- xorl %eax, %eax
- testl $96, 4(%esp)
- setne %al
- ret
-
-This should definitely be done in instcombine, canonicalizing the range
-condition into a != condition. We get this IR:
-
-define i32 @a(i32 %x) nounwind readnone {
-entry:
- %0 = and i32 %x, 127 ; <i32> [#uses=1]
- %1 = icmp ugt i32 %0, 31 ; <i1> [#uses=1]
- %2 = zext i1 %1 to i32 ; <i32> [#uses=1]
- ret i32 %2
-}
-
-Instcombine prefers to strength reduce relational comparisons to equality
-comparisons when possible, this should be another case of that. This could
-be handled pretty easily in InstCombiner::visitICmpInstWithInstAndIntCst, but it
-looks like InstCombiner::visitICmpInstWithInstAndIntCst should really already
-be redesigned to use ComputeMaskedBits and friends.
-
-
-//===---------------------------------------------------------------------===//
Testcase:
int x(int a) { return (a&0xf0)>>4; }
ICI.setOperand(0, NewAnd);
return &ICI;
}
+
+ // Replace ((X & AndCST) > RHSV) with ((X & AndCST) != 0), if any
+ // bit set in (X & AndCST) will produce a result greater than RHSV.
+ if (ICI.getPredicate() == ICmpInst::ICMP_UGT) {
+ unsigned NTZ = AndCST->getValue().countTrailingZeros();
+ if ((NTZ < AndCST->getBitWidth()) &&
+ APInt::getOneBitSet(AndCST->getBitWidth(), NTZ).ugt(RHSV))
+ return new ICmpInst(ICmpInst::ICMP_NE, LHSI,
+ Constant::getNullValue(RHS->getType()));
+ }
}
// Try to optimize things like "A[i]&42 == 0" to index computations.
; CHECK-NEXT: ret i1 true
ret i1 %cmp
}
+
+; CHECK: @test67
+; CHECK: %and = and i32 %x, 96
+; CHECK: %cmp = icmp ne i32 %and, 0
+define i1 @test67(i32 %x) nounwind uwtable {
+ %and = and i32 %x, 127
+ %cmp = icmp sgt i32 %and, 31
+ ret i1 %cmp
+}
+
+; CHECK: @test68
+; CHECK: %cmp = icmp ugt i32 %and, 30
+define i1 @test68(i32 %x) nounwind uwtable {
+ %and = and i32 %x, 127
+ %cmp = icmp sgt i32 %and, 30
+ ret i1 %cmp
+}