[PATCH] D112095: [x86] add special-case lowering for usubsat for pre-SSE4
Sanjay Patel via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Tue Oct 19 14:15:12 PDT 2021
This revision was landed with ongoing or failed builds.
This revision was automatically updated to reflect the committed changes.
Closed by commit rG92a0389b0425: [x86] add special-case lowering for usubsat for pre-SSE4 (authored by spatel).
Changed prior to commit:
https://reviews.llvm.org/D112095?vs=380773&id=380776#toc
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D112095/new/
https://reviews.llvm.org/D112095
Files:
llvm/lib/Target/X86/X86ISelLowering.cpp
llvm/test/CodeGen/X86/psubus.ll
Index: llvm/test/CodeGen/X86/psubus.ll
===================================================================
--- llvm/test/CodeGen/X86/psubus.ll
+++ llvm/test/CodeGen/X86/psubus.ll
@@ -29,6 +29,7 @@
}
; This is logically equivalent to the above.
+; usubsat X, (1 << (BW-1)) <--> (X ^ (1 << (BW-1))) & (ashr X, (BW-1))
define <8 x i16> @ashr_xor_and(<8 x i16> %x) nounwind {
; SSE-LABEL: ashr_xor_and:
@@ -127,14 +128,14 @@
ret <4 x i32> %res
}
+; usubsat X, (1 << (BW-1)) <--> (X ^ (1 << (BW-1))) & (ashr X, (BW-1))
+
define <4 x i32> @usubsat_custom(<4 x i32> %x) nounwind {
; SSE2OR3-LABEL: usubsat_custom:
; SSE2OR3: # %bb.0:
-; SSE2OR3-NEXT: movdqa {{.*#+}} xmm1 = [2147483648,2147483648,2147483648,2147483648]
-; SSE2OR3-NEXT: pxor %xmm0, %xmm1
-; SSE2OR3-NEXT: pxor %xmm2, %xmm2
-; SSE2OR3-NEXT: pcmpgtd %xmm2, %xmm1
-; SSE2OR3-NEXT: psubd {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %xmm0
+; SSE2OR3-NEXT: movdqa %xmm0, %xmm1
+; SSE2OR3-NEXT: psrad $31, %xmm1
+; SSE2OR3-NEXT: pxor {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %xmm0
; SSE2OR3-NEXT: pand %xmm1, %xmm0
; SSE2OR3-NEXT: retq
;
Index: llvm/lib/Target/X86/X86ISelLowering.cpp
===================================================================
--- llvm/lib/Target/X86/X86ISelLowering.cpp
+++ llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -28135,7 +28135,19 @@
EVT SetCCResultType =
TLI.getSetCCResultType(DAG.getDataLayout(), *DAG.getContext(), VT);
+ unsigned BitWidth = VT.getScalarSizeInBits();
if (Opcode == ISD::USUBSAT && !TLI.isOperationLegal(ISD::UMAX, VT)) {
+ // Handle a special-case with a bit-hack instead of cmp+select:
+ // usubsat X, SMIN --> (X ^ SMIN) & (X s>> BW-1)
+ ConstantSDNode *C = isConstOrConstSplat(Y, true);
+ if (C && C->getAPIntValue().isSignMask()) {
+ SDValue SignMask = DAG.getConstant(C->getAPIntValue(), DL, VT);
+ SDValue ShiftAmt = DAG.getConstant(BitWidth - 1, DL, VT);
+ SDValue Xor = DAG.getNode(ISD::XOR, DL, VT, X, SignMask);
+ SDValue Sra = DAG.getNode(ISD::SRA, DL, VT, X, ShiftAmt);
+ return DAG.getNode(ISD::AND, DL, VT, Xor, Sra);
+ }
+
// usubsat X, Y --> (X >u Y) ? X - Y : 0
SDValue Sub = DAG.getNode(ISD::SUB, DL, VT, X, Y);
SDValue Cmp = DAG.getSetCC(DL, SetCCResultType, X, Y, ISD::SETUGT);
@@ -28148,7 +28160,6 @@
if ((Opcode == ISD::SADDSAT || Opcode == ISD::SSUBSAT) &&
(!VT.isVector() || VT == MVT::v2i64)) {
- unsigned BitWidth = VT.getScalarSizeInBits();
APInt MinVal = APInt::getSignedMinValue(BitWidth);
APInt MaxVal = APInt::getSignedMaxValue(BitWidth);
SDValue Zero = DAG.getConstant(0, DL, VT);
-------------- next part --------------
A non-text attachment was scrubbed...
Name: D112095.380776.patch
Type: text/x-patch
Size: 2655 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20211019/2de526f1/attachment.bin>
More information about the llvm-commits
mailing list