[IR] allow fast-math-flags on select of FP values

This is a minimal start to correcting a problem most directly discussed in PR38086:
https://bugs.llvm.org/show_bug.cgi?id=38086

We have been hacking around a limitation for FP select patterns by using the
fast-math-flags on the condition of the select rather than the select itself.
This patch just allows FMF to appear with the 'select' opcode. No changes are
needed to "FPMathOperator" because it already includes select-of-FP because
that definition is based on the (return) value type.

Once we have this ability, we can start correcting and adding IR transforms
to use the FMF on a 'select' instruction. The instcombine and vectorizer test
diffs only show that the IRBuilder change is behaving as expected by applying
an FMF guard value to 'select'.

For reference:
rL241901 - allowed FMF with fcmp
rL255555 - allowed FMF with FP calls

Differential Revision: https://reviews.llvm.org/D61917

llvm-svn: 361401

1 files changed, 13 insertions, 1 deletions

diff --git a/llvm/lib/AsmParser/LLParser.cpp b/llvm/lib/AsmParser/LLParser.cpp
index 56012490c45..f16f6a2af49 100644
--- a/llvm/lib/AsmParser/LLParser.cpp
+++ b/llvm/lib/AsmParser/LLParser.cpp
@@ -5701,7 +5701,19 @@ int LLParser::ParseInstruction(Instruction *&Inst, BasicBlock *BB,
   case lltok::kw_inttoptr:
   case lltok::kw_ptrtoint:       return ParseCast(Inst, PFS, KeywordVal);
   // Other.
-  case lltok::kw_select:         return ParseSelect(Inst, PFS);
+  case lltok::kw_select: {
+    FastMathFlags FMF = EatFastMathFlagsIfPresent();
+    int Res = ParseSelect(Inst, PFS);
+    if (Res != 0)
+      return Res;
+    if (FMF.any()) {
+      if (!Inst->getType()->isFPOrFPVectorTy())
+        return Error(Loc, "fast-math-flags specified for select without "
+                          "floating-point scalar or vector return type");
+      Inst->setFastMathFlags(FMF);
+    }
+    return 0;
+  }
   case lltok::kw_va_arg:         return ParseVA_Arg(Inst, PFS);
   case lltok::kw_extractelement: return ParseExtractElement(Inst, PFS);
   case lltok::kw_insertelement:  return ParseInsertElement(Inst, PFS);