[PATCH] D114306: [X86] Don't combine (x86cmp (trunc (movmsk (bitcast X))), 0) if the truncate discards bits.
Craig Topper via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Fri Nov 19 21:51:36 PST 2021
This revision was landed with ongoing or failed builds.
This revision was automatically updated to reflect the committed changes.
Closed by commit rGa4373f6753fa: [X86] Don't combine (x86cmp (trunc (movmsk (bitcast X))), 0) if the truncate… (authored by craig.topper).
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D114306/new/
https://reviews.llvm.org/D114306
Files:
llvm/lib/Target/X86/X86ISelLowering.cpp
llvm/test/CodeGen/X86/pr52567.ll
Index: llvm/test/CodeGen/X86/pr52567.ll
===================================================================
--- llvm/test/CodeGen/X86/pr52567.ll
+++ llvm/test/CodeGen/X86/pr52567.ll
@@ -2,17 +2,16 @@
; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu | FileCheck %s
; The and in the test below discards half the bits from vector icmp result.
-; FIXME: The generated code is using a movmskps, but fails to discard bits
-; 2 and 3 before the testl.
+; We use a testb after a pmovmskb to examine only 8 bits.
define i32 @foo(<4 x float> %arg) {
; CHECK-LABEL: foo:
; CHECK: # %bb.0: # %bb
; CHECK-NEXT: movaps {{.*#+}} xmm1 = [1.00000005E-3,1.00000005E-3,1.00000005E-3,1.00000005E-3]
; CHECK-NEXT: cmpltps %xmm0, %xmm1
-; CHECK-NEXT: movmskps %xmm1, %ecx
+; CHECK-NEXT: pmovmskb %xmm1, %ecx
; CHECK-NEXT: xorl %eax, %eax
-; CHECK-NEXT: testl %ecx, %ecx
+; CHECK-NEXT: testb %cl, %cl
; CHECK-NEXT: sete %al
; CHECK-NEXT: retq
bb:
Index: llvm/lib/Target/X86/X86ISelLowering.cpp
===================================================================
--- llvm/lib/Target/X86/X86ISelLowering.cpp
+++ llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -44004,7 +44004,11 @@
// signbits extend down to all the sub-elements as well.
// Calling MOVMSK with the wider type, avoiding the bitcast, helps expose
// potential SimplifyDemandedBits/Elts cases.
- if (Vec.getOpcode() == ISD::BITCAST) {
+ // If we looked through a truncate that discard bits, we can't do this
+ // transform.
+ // FIXME: We could do this transform for truncates that discarded bits by
+ // inserting an AND mask between the new MOVMSK and the CMP.
+ if (Vec.getOpcode() == ISD::BITCAST && NumElts <= CmpBits) {
SDValue BC = peekThroughBitcasts(Vec);
MVT BCVT = BC.getSimpleValueType();
unsigned BCNumElts = BCVT.getVectorNumElements();
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