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[X86] Don't select (cmp (and, imm), 0) to testw

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Summary:
X86ISelDAGToDAG tries to analyze ANDs compared with 0 to optimize to narrower immediates using subregisters.

I don't think we should be optimizing to 16-bit test instructions. It goes against our normal behavior of promoting i16 operations to i32. It only saves one byte due to the need to add a 0x66 prefix. I think it would also be subject to a length changing prefix penalty in the decoders on Intel CPUs.

Reviewers: RKSimon, zvi, spatel

Reviewed By: spatel

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D38273

llvm-svn: 314474
This commit is contained in:
Craig Topper 2017-09-28 23:35:36 +00:00
parent c776b2e567
commit 22309ec191
4 changed files with 46 additions and 9 deletions
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5
lib/Target/X86/X86ISelDAGToDAG.cpp
View File

@ -3025,7 +3025,10 @@ void X86DAGToDAGISel::Select(SDNode *Node) {
}
// For example, "testl %eax, $32776" to "testw %ax, $32776".
if (isUInt<16>(Mask) && N0.getValueType() != MVT::i16 &&
// NOTE: We only want to form TESTW instructions if optimizing for
// min size. Otherwise we only save one byte and possibly get a length
// changing prefix penalty in the decoders.
if (OptForMinSize && isUInt<16>(Mask) && N0.getValueType() != MVT::i16 &&
(!(Mask & 0x8000) || hasNoSignedComparisonUses(Node))) {
SDValue Imm = CurDAG->getTargetConstant(Mask, dl, MVT::i16);
SDValue Reg = N0.getOperand(0);

4
test/CodeGen/X86/tbm_patterns.ll
View File

@ -53,7 +53,7 @@ define i32 @test_x86_tbm_bextri_u32_z2(i32 %a, i32 %b, i32 %c) nounwind {
; CHECK-LABEL: test_x86_tbm_bextri_u32_z2:
; CHECK: # BB#0:
; CHECK-NEXT: shrl $4, %edi
; CHECK-NEXT: testw $4095, %di # imm = 0xFFF
; CHECK-NEXT: testl $4095, %edi # imm = 0xFFF
; CHECK-NEXT: cmovnel %edx, %esi
; CHECK-NEXT: movl %esi, %eax
; CHECK-NEXT: retq
@ -114,7 +114,7 @@ define i64 @test_x86_tbm_bextri_u64_z2(i64 %a, i64 %b, i64 %c) nounwind {
; CHECK-LABEL: test_x86_tbm_bextri_u64_z2:
; CHECK: # BB#0:
; CHECK-NEXT: shrl $4, %edi
; CHECK-NEXT: testw $4095, %di # imm = 0xFFF
; CHECK-NEXT: testl $4095, %edi # imm = 0xFFF
; CHECK-NEXT: cmovneq %rdx, %rsi
; CHECK-NEXT: movq %rsi, %rax
; CHECK-NEXT: retq

2
test/CodeGen/X86/test-shrink-bug.ll
View File

@ -3,7 +3,7 @@
; Codegen shouldn't reduce the comparison down to testb $-1, %al
; because that changes the result of the signed test.
; PR5132
; CHECK: testw $255, %ax
; CHECK: testl $255, %eax
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-darwin10.0"

44
test/CodeGen/X86/test-shrink.ll
View File

@ -105,16 +105,33 @@ no:
ret void
}
; CHECK-64-LABEL: g64x16:
; CHECK-64: testw $-32640, %[[A0W:di|cx]]
; CHECK-64: testl $32896, %[[A0D:edi|ecx]]
; CHECK-64: ret
; CHECK-32-LABEL: g64x16:
; CHECK-32: testw $-32640, %ax
; CHECK-32: testl $32896, %eax
; CHECK-32: ret
define void @g64x16(i64 inreg %x) nounwind {
%t = and i64 %x, 32896
%s = icmp eq i64 %t, 0
br i1 %s, label %yes, label %no
yes:
call void @bar()
ret void
no:
ret void
}
; CHECK-64-LABEL: g64x16minsize:
; CHECK-64: testw $-32640, %[[A0W:di|cx]]
; CHECK-64: ret
; CHECK-32-LABEL: g64x16minsize:
; CHECK-32: testw $-32640, %ax
; CHECK-32: ret
define void @g64x16minsize(i64 inreg %x) nounwind minsize {
%t = and i64 %x, 32896
%s = icmp eq i64 %t, 0
br i1 %s, label %yes, label %no
yes:
call void @bar()
ret void
@ -122,16 +139,33 @@ no:
ret void
}
; CHECK-64-LABEL: g32x16:
; CHECK-64: testw $-32640, %[[A0W]]
; CHECK-64: testl $32896, %[[A0D]]
; CHECK-64: ret
; CHECK-32-LABEL: g32x16:
; CHECK-32: testw $-32640, %ax
; CHECK-32: testl $32896, %eax
; CHECK-32: ret
define void @g32x16(i32 inreg %x) nounwind {
%t = and i32 %x, 32896
%s = icmp eq i32 %t, 0
br i1 %s, label %yes, label %no
yes:
call void @bar()
ret void
no:
ret void
}
; CHECK-64-LABEL: g32x16minsize:
; CHECK-64: testw $-32640, %[[A0W]]
; CHECK-64: ret
; CHECK-32-LABEL: g32x16minsize:
; CHECK-32: testw $-32640, %ax
; CHECK-32: ret
define void @g32x16minsize(i32 inreg %x) nounwind minsize {
%t = and i32 %x, 32896
%s = icmp eq i32 %t, 0
br i1 %s, label %yes, label %no
yes:
call void @bar()
ret void
@ -139,7 +173,7 @@ no:
ret void
}
; CHECK-64-LABEL: g64x32:
; CHECK-64: testl $268468352, %e[[A0W]]
; CHECK-64: testl $268468352, %[[A0D]]
; CHECK-64: ret
; CHECK-32-LABEL: g64x32:
; CHECK-32: testl $268468352, %eax