[llvm] r220290 - [PowerPC] Avoid VSX FMA mutate when killed product reg = addend reg

[Bill Schmidt]

Author: wschmidt
Date: Tue Oct 21 08:02:37 2014
New Revision: 220290

URL: http://llvm.org/viewvc/llvm-project?rev=220290&view=rev
Log:
[PowerPC] Avoid VSX FMA mutate when killed product reg = addend reg

With VSX enabled, test/CodeGen/PowerPC/recipest.ll exposes a bug in
the FMA mutation pass.  If we have a situation where a killed product
register is the same register as the FMA target, such as:

   %vreg5<def,tied1> = XSNMSUBADP %vreg5<tied0>, %vreg11, %vreg5,
                       %RM<imp-use>; VSFRC:%vreg5 F8RC:%vreg11 

then the substitution makes no sense.  We end up getting a crash when
we try to extend the interval associated with the killed product
register, as there is already a live range for %vreg5 there.  This
patch just disables the mutation under those circumstances.

Since recipest.ll generates different code with VMX enabled, I've
modified that test to use -mattr=-vsx.  I've borrowed the code from
that test that exposed the bug and placed it in fma-mutate.ll, where
it tests several mutation opportunities including the "bad" one.

Added:
    llvm/trunk/test/CodeGen/PowerPC/fma-mutate.ll
Modified:
    llvm/trunk/lib/Target/PowerPC/PPCInstrInfo.cpp
    llvm/trunk/test/CodeGen/PowerPC/recipest.ll

Modified: llvm/trunk/lib/Target/PowerPC/PPCInstrInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/PowerPC/PPCInstrInfo.cpp?rev=220290&r1=220289&r2=220290&view=diff
==============================================================================
--- llvm/trunk/lib/Target/PowerPC/PPCInstrInfo.cpp (original)
+++ llvm/trunk/lib/Target/PowerPC/PPCInstrInfo.cpp Tue Oct 21 08:02:37 2014
@@ -1754,6 +1754,12 @@ protected:
 
         unsigned OldFMAReg = MI->getOperand(0).getReg();
 
+        // The transformation doesn't work well with things like:
+        //    %vreg5 = A-form-op %vreg5, %vreg11, %vreg5;
+        // so leave such things alone.
+        if (OldFMAReg == KilledProdReg)
+          continue;
+
         assert(OldFMAReg == AddendMI->getOperand(0).getReg() &&
                "Addend copy not tied to old FMA output!");
 

Added: llvm/trunk/test/CodeGen/PowerPC/fma-mutate.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/PowerPC/fma-mutate.ll?rev=220290&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/PowerPC/fma-mutate.ll (added)
+++ llvm/trunk/test/CodeGen/PowerPC/fma-mutate.ll Tue Oct 21 08:02:37 2014
@@ -0,0 +1,21 @@
+; Test several VSX FMA mutation opportunities.  The first one isn't a
+; reasonable transformation because the killed product register is the
+; same as the FMA target register.  The second one is legal.  The third
+; one doesn't fit the feeding-copy pattern.
+
+; RUN: llc < %s -mtriple=powerpc64-unknown-linux-gnu -mcpu=pwr7 -enable-unsafe-fp-math -mattr=+vsx | FileCheck %s
+target datalayout = "E-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-f128:128:128-v128:128:128-n32:64"
+target triple = "powerpc64-unknown-linux-gnu"
+
+declare double @llvm.sqrt.f64(double)
+
+define double @foo3(double %a) nounwind {
+  %r = call double @llvm.sqrt.f64(double %a)
+  ret double %r
+
+; CHECK: @foo3
+; CHECK: xsnmsubadp [[REG:[0-9]+]], {{[0-9]+}}, [[REG]]
+; CHECK: xsmaddmdp
+; CHECK: xsmaddadp
+}
+

Modified: llvm/trunk/test/CodeGen/PowerPC/recipest.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/PowerPC/recipest.ll?rev=220290&r1=220289&r2=220290&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/PowerPC/recipest.ll (original)
+++ llvm/trunk/test/CodeGen/PowerPC/recipest.ll Tue Oct 21 08:02:37 2014
@@ -1,5 +1,5 @@
-; RUN: llc < %s -mtriple=powerpc64-unknown-linux-gnu -mcpu=pwr7 -enable-unsafe-fp-math | FileCheck %s
-; RUN: llc < %s -mtriple=powerpc64-unknown-linux-gnu -mcpu=pwr7 | FileCheck -check-prefix=CHECK-SAFE %s
+; RUN: llc < %s -mtriple=powerpc64-unknown-linux-gnu -mcpu=pwr7 -enable-unsafe-fp-math -mattr=-vsx | FileCheck %s
+; RUN: llc < %s -mtriple=powerpc64-unknown-linux-gnu -mcpu=pwr7 -mattr=-vsx | FileCheck -check-prefix=CHECK-SAFE %s
 target datalayout = "E-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-f128:128:128-v128:128:128-n32:64"
 target triple = "powerpc64-unknown-linux-gnu"