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[DAGCombiner] rot i16 X, 8 --> bswap X

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We have this generic transform in IR (instcombine),
but as shown in PR41098:
http://bugs.llvm.org/PR41098
...the pattern may emerge in codegen too.

x86 has a potential refinement/reversal opportunity here,
but that should come later or needs a target hook to
avoid the transform. Converting to bswap is the more
specific form, so we should use it if it is available.
This commit is contained in:
Sanjay Patel 2020-07-13 11:35:38 -04:00
parent 217126ba1d
commit 68e3493e48
2 changed files with 68 additions and 28 deletions
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6
lib/CodeGen/SelectionDAG/DAGCombiner.cpp
View File

@ -7694,6 +7694,12 @@ SDValue DAGCombiner::visitRotate(SDNode *N) {
return DAG.getNode(N->getOpcode(), dl, VT, N0, Amt);
}
// rot i16 X, 8 --> bswap X
auto *RotAmtC = isConstOrConstSplat(N1);
if (RotAmtC && RotAmtC->getAPIntValue() == 8 &&
VT.getScalarSizeInBits() == 16 && hasOperation(ISD::BSWAP, VT))
return DAG.getNode(ISD::BSWAP, dl, VT, N0);
// Simplify the operands using demanded-bits information.
if (SimplifyDemandedBits(SDValue(N, 0)))
return SDValue(N, 0);

90
test/CodeGen/X86/rot16.ll
View File

@ -234,11 +234,16 @@ define i16 @rot16_trunc(i32 %x, i32 %y) nounwind {
}
define i16 @rotate16(i16 %x) {
; X32-LABEL: rotate16:
; X32: # %bb.0:
; X32-NEXT: movzwl {{[0-9]+}}(%esp), %eax
; X32-NEXT: rolw $8, %ax
; X32-NEXT: retl
; BASE32-LABEL: rotate16:
; BASE32: # %bb.0:
; BASE32-NEXT: movzwl {{[0-9]+}}(%esp), %eax
; BASE32-NEXT: rolw $8, %ax
; BASE32-NEXT: retl
;
; MOVBE32-LABEL: rotate16:
; MOVBE32: # %bb.0:
; MOVBE32-NEXT: movbew {{[0-9]+}}(%esp), %ax
; MOVBE32-NEXT: retl
;
; X64-LABEL: rotate16:
; X64: # %bb.0:
@ -250,17 +255,32 @@ define i16 @rotate16(i16 %x) {
ret i16 %r
}
; TODO: Should this always be rolw with memory operand?
define void @rotate16_in_place_memory(i8* %p) {
; X32-LABEL: rotate16_in_place_memory:
; X32: # %bb.0:
; X32-NEXT: movl {{[0-9]+}}(%esp), %eax
; X32-NEXT: rolw $8, (%eax)
; X32-NEXT: retl
; BASE32-LABEL: rotate16_in_place_memory:
; BASE32: # %bb.0:
; BASE32-NEXT: movl {{[0-9]+}}(%esp), %eax
; BASE32-NEXT: rolw $8, (%eax)
; BASE32-NEXT: retl
;
; X64-LABEL: rotate16_in_place_memory:
; X64: # %bb.0:
; X64-NEXT: rolw $8, (%rdi)
; X64-NEXT: retq
; MOVBE32-LABEL: rotate16_in_place_memory:
; MOVBE32: # %bb.0:
; MOVBE32-NEXT: movl {{[0-9]+}}(%esp), %eax
; MOVBE32-NEXT: movzwl (%eax), %ecx
; MOVBE32-NEXT: movbew %cx, (%eax)
; MOVBE32-NEXT: retl
;
; BASE64-LABEL: rotate16_in_place_memory:
; BASE64: # %bb.0:
; BASE64-NEXT: rolw $8, (%rdi)
; BASE64-NEXT: retq
;
; MOVBE64-LABEL: rotate16_in_place_memory:
; MOVBE64: # %bb.0:
; MOVBE64-NEXT: movzwl (%rdi), %eax
; MOVBE64-NEXT: movbew %ax, (%rdi)
; MOVBE64-NEXT: retq
%p0 = getelementptr i8, i8* %p, i64 0
%p1 = getelementptr i8, i8* %p, i64 1
%i0 = load i8, i8* %p0, align 1
@ -271,21 +291,35 @@ define void @rotate16_in_place_memory(i8* %p) {
}
define void @rotate16_memory(i8* %p, i8* %q) {
; X32-LABEL: rotate16_memory:
; X32: # %bb.0:
; X32-NEXT: movl {{[0-9]+}}(%esp), %eax
; X32-NEXT: movl {{[0-9]+}}(%esp), %ecx
; X32-NEXT: movzwl (%ecx), %ecx
; X32-NEXT: rolw $8, %cx
; X32-NEXT: movw %cx, (%eax)
; X32-NEXT: retl
; BASE32-LABEL: rotate16_memory:
; BASE32: # %bb.0:
; BASE32-NEXT: movl {{[0-9]+}}(%esp), %eax
; BASE32-NEXT: movl {{[0-9]+}}(%esp), %ecx
; BASE32-NEXT: movzwl (%ecx), %ecx
; BASE32-NEXT: rolw $8, %cx
; BASE32-NEXT: movw %cx, (%eax)
; BASE32-NEXT: retl
;
; X64-LABEL: rotate16_memory:
; X64: # %bb.0:
; X64-NEXT: movzwl (%rdi), %eax
; X64-NEXT: rolw $8, %ax
; X64-NEXT: movw %ax, (%rsi)
; X64-NEXT: retq
; MOVBE32-LABEL: rotate16_memory:
; MOVBE32: # %bb.0:
; MOVBE32-NEXT: movl {{[0-9]+}}(%esp), %eax
; MOVBE32-NEXT: movl {{[0-9]+}}(%esp), %ecx
; MOVBE32-NEXT: movzwl (%ecx), %ecx
; MOVBE32-NEXT: movbew %cx, (%eax)
; MOVBE32-NEXT: retl
;
; BASE64-LABEL: rotate16_memory:
; BASE64: # %bb.0:
; BASE64-NEXT: movzwl (%rdi), %eax
; BASE64-NEXT: rolw $8, %ax
; BASE64-NEXT: movw %ax, (%rsi)
; BASE64-NEXT: retq
;
; MOVBE64-LABEL: rotate16_memory:
; MOVBE64: # %bb.0:
; MOVBE64-NEXT: movzwl (%rdi), %eax
; MOVBE64-NEXT: movbew %ax, (%rsi)
; MOVBE64-NEXT: retq
%p0 = getelementptr i8, i8* %p, i64 0
%p1 = getelementptr i8, i8* %p, i64 1
%q0 = getelementptr i8, i8* %q, i64 0