when we know the signbit of an input to uint_to_fp is zero,

change it to sint_to_fp on targets where that is cheaper (and
visaversa of course).  This allows us to compile uint_to_fp to:

_test:
	movl	4(%esp), %eax
	shrl	$23, %eax
	cvtsi2ss	%eax, %xmm0
	movl	8(%esp), %eax
	movss	%xmm0, (%eax)
	ret

instead of:

	.align	3
LCPI1_0:					##  double
	.long	0	## double least significant word 4.5036e+15
	.long	1127219200	## double most significant word 4.5036e+15
	.text
	.align	4,0x90
	.globl	_test
_test:
	subl	$12, %esp
	movl	16(%esp), %eax
	shrl	$23, %eax
	movl	%eax, (%esp)
	movl	$1127219200, 4(%esp)
	movsd	(%esp), %xmm0
	subsd	LCPI1_0, %xmm0
	cvtsd2ss	%xmm0, %xmm0
	movl	20(%esp), %eax
	movss	%xmm0, (%eax)
	addl	$12, %esp
	ret




git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@52747 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 39 insertions, 3 deletions

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index c07ad27baa..d39d43e577 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -3844,10 +3844,22 @@ SDOperand DAGCombiner::visitSINT_TO_FP(SDNode *N) {
   SDOperand N0 = N->getOperand(0);
   ConstantSDNode *N0C = dyn_cast<ConstantSDNode>(N0);
   MVT VT = N->getValueType(0);
-  
+  MVT OpVT = N0.getValueType();
+
   // fold (sint_to_fp c1) -> c1fp
-  if (N0C && N0.getValueType() != MVT::ppcf128)
+  if (N0C && OpVT != MVT::ppcf128)
     return DAG.getNode(ISD::SINT_TO_FP, VT, N0);
+  
+  // If the input is a legal type, and SINT_TO_FP is not legal on this target,
+  // but UINT_TO_FP is legal on this target, try to convert.
+  if (TLI.isTypeLegal(OpVT) && !TLI.isOperationLegal(ISD::SINT_TO_FP, OpVT) &&
+      TLI.isOperationLegal(ISD::UINT_TO_FP, OpVT)) {
+    // If the sign bit is known to be zero, we can change this to UINT_TO_FP. 
+    if (DAG.SignBitIsZero(N0))
+      return DAG.getNode(ISD::UINT_TO_FP, VT, N0);
+  }
+  
+  
   return SDOperand();
 }
 
@@ -3855,10 +3867,21 @@ SDOperand DAGCombiner::visitUINT_TO_FP(SDNode *N) {
   SDOperand N0 = N->getOperand(0);
   ConstantSDNode *N0C = dyn_cast<ConstantSDNode>(N0);
   MVT VT = N->getValueType(0);
+  MVT OpVT = N0.getValueType();
 
   // fold (uint_to_fp c1) -> c1fp
-  if (N0C && N0.getValueType() != MVT::ppcf128)
+  if (N0C && OpVT != MVT::ppcf128)
     return DAG.getNode(ISD::UINT_TO_FP, VT, N0);
+  
+  // If the input is a legal type, and UINT_TO_FP is not legal on this target,
+  // but SINT_TO_FP is legal on this target, try to convert.
+  if (TLI.isTypeLegal(OpVT) && !TLI.isOperationLegal(ISD::UINT_TO_FP, OpVT) &&
+      TLI.isOperationLegal(ISD::SINT_TO_FP, OpVT)) {
+    // If the sign bit is known to be zero, we can change this to SINT_TO_FP. 
+    if (DAG.SignBitIsZero(N0))
+      return DAG.getNode(ISD::SINT_TO_FP, VT, N0);
+  }
+  
   return SDOperand();
 }
 
diff --git a/test/CodeGen/X86/uint_to_fp.ll b/test/CodeGen/X86/uint_to_fp.ll
new file mode 100644
index 0000000000..3ea7a947b9
--- /dev/null
+++ b/test/CodeGen/X86/uint_to_fp.ll
@@ -0,0 +1,13 @@
+; RUN: llvm-as < %s | llc -march=x86 -mcpu=yonah | not grep {sub.*esp}
+; rdar://6034396
+
+target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
+target triple = "i386-apple-darwin8"
+
+define void @test(i32 %x, float* %y) nounwind  {
+entry:
+	lshr i32 %x, 23		; <i32>:0 [#uses=1]
+	uitofp i32 %0 to float		; <float>:1 [#uses=1]
+	store float %1, float* %y
+	ret void
+}