[PowerPC] Allow wa inline asm to also accept floating point arguments

GCC documentation for the `wa` constraint states that:
```
wa

    A VSX register (VSR), vs0…vs63. This is either an FPR (vs0…vs31 are f0…f31)
    or a VR (vs32…vs63 are v0…v31).
```
This technically means that we could accept floating point parameters. In fact,
gcc itself does. The following testcase compiles and runs on all PPC platforms with GCC,
whereas clang/llc will assert:
```
#include <stdio.h>
double foo ( vector double a ) {
  double b, c;
  asm("xvabsdp  %x0, %x2        \n"
             "xxsldwi  %x1, %x0, %x0, 2 \n"
      :  "+wa"    (b),
         "=wa"    (c)
      :  "wa"    (a)
      );
  return b+c;
}
int main(void) {
  vector double a = {-3., -4.};
  double t = foo( a );
  printf("%g\n", t);
}
```
This patch allows clang/llc to build and run this testcase.

Reviewed By: nemanjai, #powerpc

Differential Revision: https://reviews.llvm.org/D103409

diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
index 013ce0c..2dc948c 100644 (file)
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -15648,7 +15648,13 @@ PPCTargetLowering::getRegForInlineAsmConstraint(const TargetRegisterInfo *TRI,
   } else if ((Constraint == "wa" || Constraint == "wd" ||
              Constraint == "wf" || Constraint == "wi") &&
              Subtarget.hasVSX()) {
-    return std::make_pair(0U, &PPC::VSRCRegClass);
+    // A VSX register for either a scalar (FP) or vector. There is no
+    // support for single precision scalars on subtargets prior to Power8.
+    if (VT.isVector())
+      return std::make_pair(0U, &PPC::VSRCRegClass);
+    if (VT == MVT::f32 && Subtarget.hasP8Vector())
+      return std::make_pair(0U, &PPC::VSSRCRegClass);
+    return std::make_pair(0U, &PPC::VSFRCRegClass);
   } else if ((Constraint == "ws" || Constraint == "ww") && Subtarget.hasVSX()) {
     if (VT == MVT::f32 && Subtarget.hasP8Vector())
       return std::make_pair(0U, &PPC::VSSRCRegClass);

diff --git a/llvm/test/CodeGen/PowerPC/wa-asm-fpr.ll b/llvm/test/CodeGen/PowerPC/wa-asm-fpr.ll
new file mode 100644 (file)
index 0000000..c4ec051
--- /dev/null
+++ b/llvm/test/CodeGen/PowerPC/wa-asm-fpr.ll
@@ -0,0 +1,22 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN:  llc -mtriple powerpc64le-linux-gnu --ppc-asm-full-reg-names \
+; RUN:      -verify-machineinstrs -mattr=vsx -mattr=altivec < %s | \
+; RUN:  FileCheck %s
+
+define double @foo(<2 x double> %a) {
+; CHECK-LABEL: foo:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    #APP
+; CHECK-NEXT:    xvabsdp vs0, vs34
+; CHECK-NEXT:    xxsldwi vs1, vs0, vs0, 2
+; CHECK-EMPTY:
+; CHECK-NEXT:    #NO_APP
+; CHECK-NEXT:    xsadddp f1, f0, f1
+; CHECK-NEXT:    blr
+entry:
+  %0 = call { double, double } asm "xvabsdp  ${0:x}, ${2:x}        \0Axxsldwi  ${1:x}, ${0:x}, ${0:x}, 2 \0A", "=^wa,=^wa,^wa,0"(<2 x double> %a, double undef)
+  %asmresult = extractvalue { double, double } %0, 0
+  %asmresult1 = extractvalue { double, double } %0, 1
+  %add = fadd double %asmresult, %asmresult1
+  ret double %add
+}