add fast-math-flags to 'call' instructions (PR21290)

This patch adds optional fast-math-flags (the same that apply to fmul/fadd/fsub/fdiv/frem/fcmp)
to call instructions in IR. Follow-up patches would use these flags in LibCallSimplifier, add 
support to clang, and extend FMF to the DAG for calls.

Motivating example:

%y = fmul fast float %x, %x
%z = tail call float @sqrtf(float %y)

We'd like to be able to optimize sqrt(x*x) into fabs(x). We do this today using a function-wide
attribute for unsafe-math, but we really want to trigger on the instructions themselves:

%z = tail call fast float @sqrtf(float %y)

because in an LTO build it's possible that calls with fast semantics have been inlined into a
function with non-fast semantics.

The code changes and tests are based on the recent commits that added "notail":
http://reviews.llvm.org/rL252368

and added FMF to fcmp:
http://reviews.llvm.org/rL241901

Differential Revision: http://reviews.llvm.org/D14707

llvm-svn: 255555

1 files changed, 14 insertions, 1 deletions

diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
index 210ffd8d912..d59f12898e9 100644
--- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -5006,7 +5006,7 @@ std::error_code BitcodeReader::parseFunctionBody(Function *F) {
       break;
     }
     case bitc::FUNC_CODE_INST_CALL: {
-      // CALL: [paramattrs, cc, fnty, fnid, arg0, arg1...]
+      // CALL: [paramattrs, cc, fmf, fnty, fnid, arg0, arg1...]
       if (Record.size() < 3)
         return error("Invalid record");
 
@@ -5014,6 +5014,13 @@ std::error_code BitcodeReader::parseFunctionBody(Function *F) {
       AttributeSet PAL = getAttributes(Record[OpNum++]);
       unsigned CCInfo = Record[OpNum++];
 
+      FastMathFlags FMF;
+      if ((CCInfo >> bitc::CALL_FMF) & 1) {
+        FMF = getDecodedFastMathFlags(Record[OpNum++]);
+        if (!FMF.any())
+          return error("Fast math flags indicator set for call with no FMF");
+      }
+
       FunctionType *FTy = nullptr;
       if (CCInfo >> bitc::CALL_EXPLICIT_TYPE & 1 &&
           !(FTy = dyn_cast<FunctionType>(getTypeByID(Record[OpNum++]))))
@@ -5075,6 +5082,12 @@ std::error_code BitcodeReader::parseFunctionBody(Function *F) {
         TCK = CallInst::TCK_NoTail;
       cast<CallInst>(I)->setTailCallKind(TCK);
       cast<CallInst>(I)->setAttributes(PAL);
+      if (FMF.any()) {
+        if (!isa<FPMathOperator>(I))
+          return error("Fast-math-flags specified for call without "
+                       "floating-point scalar or vector return type");
+        I->setFastMathFlags(FMF);
+      }
       break;
     }
     case bitc::FUNC_CODE_INST_VAARG: { // VAARG: [valistty, valist, instty]