[PATCH] D17414: Fix incorrect selection of AVX512 sqrt when OptForSize is on

[Dimitry Andric via llvm-commits]

dim created this revision.
dim added reviewers: joker.eph, grosbach, resistor.
dim added a subscriber: llvm-commits.

When optimizing for size, sqrt calls can be incorrectly selected as
AVX512 VSQRT instructions.  This is because X86InstrAVX512.td has a
`Requires<[OptForSize]>` in its `avx512_sqrt_scalar` multiclass
definition.  Even if the target does not support AVX512, the class can
apparently still be chosen, leading to an incorrect selection of
`vsqrtss`.

In PR26625, this lead to an assertion: Reg >= X86::FP0 && Reg <=
X86::FP6 && "Expected FP register!", because the `vsqrtss` instruction
requires an XMM register, which is not available on i686 CPUs.

http://reviews.llvm.org/D17414

Files:
  lib/Target/X86/X86InstrAVX512.td
  test/CodeGen/X86/pr26625.ll

Index: test/CodeGen/X86/pr26625.ll
===================================================================
--- /dev/null
+++ test/CodeGen/X86/pr26625.ll
@@ -0,0 +1,20 @@
+; RUN: llc < %s -mcpu=i686 2>&1 | FileCheck %s
+; PR26625
+
+target datalayout = "e-m:e-p:32:32-f64:32:64-f80:32-n8:16:32-S128"
+target triple = "i386"
+
+define float @x0(float %f) #0 {
+entry:
+  %call = tail call float @sqrtf(float %f) #1
+  ret float %call
+; CHECK-LABEL: x0:
+; CHECK: flds
+; CHECK-NEXT: fsqrt
+; CHECK-NOT: vsqrtss
+}
+
+declare float @sqrtf(float) #0
+
+attributes #0 = { nounwind optsize readnone }
+attributes #1 = { nounwind optsize readnone }
Index: lib/Target/X86/X86InstrAVX512.td
===================================================================
--- lib/Target/X86/X86InstrAVX512.td
+++ lib/Target/X86/X86InstrAVX512.td
@@ -6005,7 +6005,7 @@
 
   def : Pat<(_.EltVT (OpNode (load addr:$src))),
             (!cast<Instruction>(NAME#SUFF#Zm)
-                (_.EltVT (IMPLICIT_DEF)), addr:$src)>, Requires<[OptForSize]>;
+                (_.EltVT (IMPLICIT_DEF)), addr:$src)>, Requires<[HasAVX512, OptForSize]>;
 }
 
 multiclass avx512_sqrt_scalar_all<bits<8> opc, string OpcodeStr> {


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