[mips] Tighten FastISel restrictions

LLVM PR/29052 highlighted that FastISel for MIPS attempted to lower
arguments assuming that it was using the paired 32bit registers to
perform operations for f64. This mode of operation is not supported
for MIPSR6.

This patch resolves the reported issue by adding additional checks
for unsupported floating point unit configuration.

Thanks to mike.k for reporting this issue!

Reviewers: seanbruno, vkalintiris

Differential Review: https://reviews.llvm.org/D23795

llvm-svn: 280706

1 files changed, 17 insertions, 1 deletions

diff --git a/llvm/lib/Target/Mips/MipsFastISel.cpp b/llvm/lib/Target/Mips/MipsFastISel.cpp
index e7b11392d0b..94531642492 100644
--- a/llvm/lib/Target/Mips/MipsFastISel.cpp
+++ b/llvm/lib/Target/Mips/MipsFastISel.cpp
@@ -976,9 +976,13 @@ bool MipsFastISel::selectFPExt(const Instruction *I) {
 bool MipsFastISel::selectSelect(const Instruction *I) {
   assert(isa<SelectInst>(I) && "Expected a select instruction.");
 
+  DEBUG(dbgs() << "selectSelect\n");
+
   MVT VT;
-  if (!isTypeSupported(I->getType(), VT))
+  if (!isTypeSupported(I->getType(), VT) || UnsupportedFPMode) {
+    DEBUG(dbgs() << ".. .. gave up (!isTypeSupported || UnsupportedFPMode)\n");
     return false;
+  }
 
   unsigned CondMovOpc;
   const TargetRegisterClass *RC;
@@ -1376,6 +1380,10 @@ bool MipsFastISel::fastLowerArguments() {
       break;
 
     case MVT::f64:
+      if (UnsupportedFPMode) {
+        DEBUG(dbgs() << ".. .. gave up (UnsupportedFPMode\n");
+        return false;
+      }
       if (NextAFGR64 == AFGR64ArgRegs.end()) {
         DEBUG(dbgs() << ".. .. gave up (ran out of AFGR64 arguments)\n");
         return false;
@@ -1617,6 +1625,8 @@ bool MipsFastISel::selectRet(const Instruction *I) {
   const Function &F = *I->getParent()->getParent();
   const ReturnInst *Ret = cast<ReturnInst>(I);
 
+  DEBUG(dbgs() << "selectRet\n");
+
   if (!FuncInfo.CanLowerReturn)
     return false;
 
@@ -1677,6 +1687,12 @@ bool MipsFastISel::selectRet(const Instruction *I) {
     if (RVVT == MVT::f128)
       return false;
 
+    // Do not handle FGR64 returns for now.
+    if (RVVT == MVT::f64 && UnsupportedFPMode) {
+      DEBUG(dbgs() << ".. .. gave up (UnsupportedFPMode\n");
+      return false;
+    }
+
     MVT DestVT = VA.getValVT();
     // Special handling for extended integers.
     if (RVVT != DestVT) {