[x86] set default reciprocal (division and square root) codegen to match GCC

D8982 ( checked in at http://reviews.llvm.org/rL239001 ) added command-line
options to allow reciprocal estimate instructions to be used in place of
divisions and square roots.

This patch changes the default settings for x86 targets to allow that recip
codegen (except for scalar division because that breaks too much code) when
using -ffast-math or its equivalent.

This matches GCC behavior for this kind of codegen.

Differential Revision: http://reviews.llvm.org/D10396

llvm-svn: 240310

diff --git a/llvm/lib/Target/X86/X86TargetMachine.cpp b/llvm/lib/Target/X86/X86TargetMachine.cpp
index 3d6eb4f..fb9cb4b 100644 (file)
--- a/llvm/lib/Target/X86/X86TargetMachine.cpp
+++ b/llvm/lib/Target/X86/X86TargetMachine.cpp
@@ -110,12 +110,15 @@ X86TargetMachine::X86TargetMachine(const Target &T, const Triple &TT,
   if (Subtarget.isTargetWin64())
     this->Options.TrapUnreachable = true;
 
-  // TODO: By default, all reciprocal estimate operations are off because
-  // that matches the behavior before TargetRecip was added (except for btver2
-  // which used subtarget features to enable this type of codegen).
-  // We should change this to match GCC behavior where everything but
-  // scalar division estimates are turned on by default with -ffast-math.
-  this->Options.Reciprocals.setDefaults("all", false, 1);
+  // By default (and when -ffast-math is on), enable estimate codegen for
+  // everything except scalar division. By default, use 1 refinement step for
+  // all operations. Defaults may be overridden by using command-line options.
+  // Scalar division estimates are disabled because they break too much
+  // real-world code. These defaults match GCC behavior.
+  this->Options.Reciprocals.setDefaults("sqrtf", true, 1);
+  this->Options.Reciprocals.setDefaults("divf", false, 1);
+  this->Options.Reciprocals.setDefaults("vec-sqrtf", true, 1);
+  this->Options.Reciprocals.setDefaults("vec-divf", true, 1);
 
   initAsmInfo();
 }

diff --git a/llvm/test/CodeGen/X86/recip-fastmath.ll b/llvm/test/CodeGen/X86/recip-fastmath.ll
index 7f1521a..8e02dad 100644 (file)
--- a/llvm/test/CodeGen/X86/recip-fastmath.ll
+++ b/llvm/test/CodeGen/X86/recip-fastmath.ll
@@ -1,4 +1,4 @@
-; RUN: llc < %s -mtriple=x86_64-unknown-unknown -mattr=sse2 | FileCheck %s
+; RUN: llc < %s -mtriple=x86_64-unknown-unknown -mattr=sse2 -recip=!divf,!vec-divf | FileCheck %s --check-prefix=NORECIP
 ; RUN: llc < %s -mtriple=x86_64-unknown-unknown -mattr=avx -recip=divf,vec-divf | FileCheck %s --check-prefix=RECIP
 ; RUN: llc < %s -mtriple=x86_64-unknown-unknown -mattr=avx -recip=divf:2,vec-divf:2 | FileCheck %s --check-prefix=REFINE
 
@@ -14,11 +14,11 @@ define float @reciprocal_estimate(float %x) #0 {
   %div = fdiv fast float 1.0, %x
   ret float %div
 
-; CHECK-LABEL: reciprocal_estimate:
-; CHECK: movss
-; CHECK-NEXT: divss
-; CHECK-NEXT: movaps
-; CHECK-NEXT: retq
+; NORECIP-LABEL: reciprocal_estimate:
+; NORECIP: movss
+; NORECIP-NEXT: divss
+; NORECIP-NEXT: movaps
+; NORECIP-NEXT: retq
 
 ; RECIP-LABEL: reciprocal_estimate:
 ; RECIP: vrcpss
@@ -45,11 +45,11 @@ define <4 x float> @reciprocal_estimate_v4f32(<4 x float> %x) #0 {
   %div = fdiv fast <4 x float> <float 1.0, float 1.0, float 1.0, float 1.0>, %x
   ret <4 x float> %div
 
-; CHECK-LABEL: reciprocal_estimate_v4f32:
-; CHECK: movaps
-; CHECK-NEXT: divps
-; CHECK-NEXT: movaps
-; CHECK-NEXT: retq
+; NORECIP-LABEL: reciprocal_estimate_v4f32:
+; NORECIP: movaps
+; NORECIP-NEXT: divps
+; NORECIP-NEXT: movaps
+; NORECIP-NEXT: retq
 
 ; RECIP-LABEL: reciprocal_estimate_v4f32:
 ; RECIP: vrcpps
@@ -76,14 +76,14 @@ define <8 x float> @reciprocal_estimate_v8f32(<8 x float> %x) #0 {
   %div = fdiv fast <8 x float> <float 1.0, float 1.0, float 1.0, float 1.0, float 1.0, float 1.0, float 1.0, float 1.0>, %x
   ret <8 x float> %div
 
-; CHECK-LABEL: reciprocal_estimate_v8f32:
-; CHECK: movaps
-; CHECK: movaps
-; CHECK-NEXT: divps
-; CHECK-NEXT: divps
-; CHECK-NEXT: movaps
-; CHECK-NEXT: movaps
-; CHECK-NEXT: retq
+; NORECIP-LABEL: reciprocal_estimate_v8f32:
+; NORECIP: movaps
+; NORECIP: movaps
+; NORECIP-NEXT: divps
+; NORECIP-NEXT: divps
+; NORECIP-NEXT: movaps
+; NORECIP-NEXT: movaps
+; NORECIP-NEXT: retq
 
 ; RECIP-LABEL: reciprocal_estimate_v8f32:
 ; RECIP: vrcpps

diff --git a/llvm/test/CodeGen/X86/sqrt-fastmath.ll b/llvm/test/CodeGen/X86/sqrt-fastmath.ll
index 373fa53..0f8d9f4 100644 (file)
--- a/llvm/test/CodeGen/X86/sqrt-fastmath.ll
+++ b/llvm/test/CodeGen/X86/sqrt-fastmath.ll
@@ -1,4 +1,4 @@
-; RUN: llc < %s -mtriple=x86_64-unknown-unknown -mattr=sse2 | FileCheck %s
+; RUN: llc < %s -mtriple=x86_64-unknown-unknown -mattr=sse2 -recip=!sqrtf,!vec-sqrtf,!divf,!vec-divf | FileCheck %s --check-prefix=NORECIP
 ; RUN: llc < %s -mtriple=x86_64-unknown-unknown -mattr=avx -recip=sqrtf,vec-sqrtf | FileCheck %s --check-prefix=ESTIMATE
 
 declare double @__sqrt_finite(double) #0
@@ -10,10 +10,10 @@ declare <8 x float> @llvm.sqrt.v8f32(<8 x float>) #0
 
 
 define double @fd(double %d) #0 {
-; CHECK-LABEL: fd:
-; CHECK:       # BB#0:
-; CHECK-NEXT:    sqrtsd %xmm0, %xmm0
-; CHECK-NEXT:    retq
+; NORECIP-LABEL: fd:
+; NORECIP:       # BB#0:
+; NORECIP-NEXT:    sqrtsd %xmm0, %xmm0
+; NORECIP-NEXT:    retq
 ;
 ; ESTIMATE-LABEL: fd:
 ; ESTIMATE:       # BB#0:
@@ -25,10 +25,10 @@ define double @fd(double %d) #0 {
 
 
 define float @ff(float %f) #0 {
-; CHECK-LABEL: ff:
-; CHECK:       # BB#0:
-; CHECK-NEXT:    sqrtss %xmm0, %xmm0
-; CHECK-NEXT:    retq
+; NORECIP-LABEL: ff:
+; NORECIP:       # BB#0:
+; NORECIP-NEXT:    sqrtss %xmm0, %xmm0
+; NORECIP-NEXT:    retq
 ;
 ; ESTIMATE-LABEL: ff:
 ; ESTIMATE:       # BB#0:
@@ -49,11 +49,11 @@ define float @ff(float %f) #0 {
 
 
 define x86_fp80 @fld(x86_fp80 %ld) #0 {
-; CHECK-LABEL: fld:
-; CHECK:       # BB#0:
-; CHECK-NEXT:    fldt {{[0-9]+}}(%rsp)
-; CHECK-NEXT:    fsqrt
-; CHECK-NEXT:    retq
+; NORECIP-LABEL: fld:
+; NORECIP:       # BB#0:
+; NORECIP-NEXT:    fldt {{[0-9]+}}(%rsp)
+; NORECIP-NEXT:    fsqrt
+; NORECIP-NEXT:    retq
 ;
 ; ESTIMATE-LABEL: fld:
 ; ESTIMATE:       # BB#0:
@@ -67,12 +67,12 @@ define x86_fp80 @fld(x86_fp80 %ld) #0 {
 
 
 define float @reciprocal_square_root(float %x) #0 {
-; CHECK-LABEL: reciprocal_square_root:
-; CHECK:       # BB#0:
-; CHECK-NEXT:    sqrtss %xmm0, %xmm1
-; CHECK-NEXT:    movss {{.*#+}} xmm0 = mem[0],zero,zero,zero
-; CHECK-NEXT:    divss %xmm1, %xmm0
-; CHECK-NEXT:    retq
+; NORECIP-LABEL: reciprocal_square_root:
+; NORECIP:       # BB#0:
+; NORECIP-NEXT:    sqrtss %xmm0, %xmm1
+; NORECIP-NEXT:    movss {{.*#+}} xmm0 = mem[0],zero,zero,zero
+; NORECIP-NEXT:    divss %xmm1, %xmm0
+; NORECIP-NEXT:    retq
 ;
 ; ESTIMATE-LABEL: reciprocal_square_root:
 ; ESTIMATE:       # BB#0:
@@ -89,12 +89,12 @@ define float @reciprocal_square_root(float %x) #0 {
 }
 
 define <4 x float> @reciprocal_square_root_v4f32(<4 x float> %x) #0 {
-; CHECK-LABEL: reciprocal_square_root_v4f32:
-; CHECK:       # BB#0:
-; CHECK-NEXT:    sqrtps %xmm0, %xmm1
-; CHECK-NEXT:    movaps {{.*#+}} xmm0 = [1.000000e+00,1.000000e+00,1.000000e+00,1.000000e+00]
-; CHECK-NEXT:    divps %xmm1, %xmm0
-; CHECK-NEXT:    retq
+; NORECIP-LABEL: reciprocal_square_root_v4f32:
+; NORECIP:       # BB#0:
+; NORECIP-NEXT:    sqrtps %xmm0, %xmm1
+; NORECIP-NEXT:    movaps {{.*#+}} xmm0 = [1.000000e+00,1.000000e+00,1.000000e+00,1.000000e+00]
+; NORECIP-NEXT:    divps %xmm1, %xmm0
+; NORECIP-NEXT:    retq
 ;
 ; ESTIMATE-LABEL: reciprocal_square_root_v4f32:
 ; ESTIMATE:       # BB#0:
@@ -111,15 +111,15 @@ define <4 x float> @reciprocal_square_root_v4f32(<4 x float> %x) #0 {
 }
 
 define <8 x float> @reciprocal_square_root_v8f32(<8 x float> %x) #0 {
-; CHECK-LABEL: reciprocal_square_root_v8f32:
-; CHECK:       # BB#0:
-; CHECK-NEXT:    sqrtps %xmm1, %xmm2
-; CHECK-NEXT:    sqrtps %xmm0, %xmm3
-; CHECK-NEXT:    movaps {{.*#+}} xmm1 = [1.000000e+00,1.000000e+00,1.000000e+00,1.000000e+00]
-; CHECK-NEXT:    movaps %xmm1, %xmm0
-; CHECK-NEXT:    divps %xmm3, %xmm0
-; CHECK-NEXT:    divps %xmm2, %xmm1
-; CHECK-NEXT:    retq
+; NORECIP-LABEL: reciprocal_square_root_v8f32:
+; NORECIP:       # BB#0:
+; NORECIP-NEXT:    sqrtps %xmm1, %xmm2
+; NORECIP-NEXT:    sqrtps %xmm0, %xmm3
+; NORECIP-NEXT:    movaps {{.*#+}} xmm1 = [1.000000e+00,1.000000e+00,1.000000e+00,1.000000e+00]
+; NORECIP-NEXT:    movaps %xmm1, %xmm0
+; NORECIP-NEXT:    divps %xmm3, %xmm0
+; NORECIP-NEXT:    divps %xmm2, %xmm1
+; NORECIP-NEXT:    retq
 ;
 ; ESTIMATE-LABEL: reciprocal_square_root_v8f32:
 ; ESTIMATE:       # BB#0: