[PATCH] D24815: [clang] make reciprocal estimate codegen a function attribute

[Sanjay Patel via cfe-commits]

spatel created this revision.
spatel added reviewers: echristo, evandro, hfinkel.
spatel added a subscriber: cfe-commits.
Herald added subscribers: mehdi_amini, mcrosier.

Technically, I suppose this patch is independent of the upcoming llvm sibling patch because we can still pass 'check-all' with this alone. But this patch should be tightly coupled with that patch when committed because there's nothing currently in llvm to read this new function attribute string.

The motivation for the change is that we can't have pseudo-global settings for codegen living in TargetOptions because that doesn't work with LTO. And yet, there are so many others there...

Ideally, these reciprocal attributes will be moved to the instruction-level via FMF, metadata, or something else. But making them function attributes is at least an improvement over the current mess.

https://reviews.llvm.org/D24815

Files:
  lib/CodeGen/BackendUtil.cpp
  lib/CodeGen/CGCall.cpp
  test/CodeGen/attr-mrecip.c

Index: test/CodeGen/attr-mrecip.c
===================================================================
--- test/CodeGen/attr-mrecip.c
+++ test/CodeGen/attr-mrecip.c
@@ -0,0 +1,7 @@
+// RUN: %clang_cc1 -mrecip=!sqrtf,vec-divf:3 -disable-llvm-optzns -emit-llvm %s -o - | FileCheck %s
+
+int baz(int a) { return 4; }
+
+// CHECK: baz{{.*}} #0
+// CHECK: #0 = {{.*}}"mrecip"="!sqrtf,vec-divf:3"
+
Index: lib/CodeGen/CGCall.cpp
===================================================================
--- lib/CodeGen/CGCall.cpp
+++ lib/CodeGen/CGCall.cpp
@@ -1730,6 +1730,9 @@
 
     FuncAttrs.addAttribute("no-trapping-math",
                            llvm::toStringRef(CodeGenOpts.NoTrappingMath));
+
+    // TODO: Are these all needed?
+    // unsafe/inf/nan/nsz are handled by instruction-level FastMathFlags.
     FuncAttrs.addAttribute("no-infs-fp-math",
                            llvm::toStringRef(CodeGenOpts.NoInfsFPMath));
     FuncAttrs.addAttribute("no-nans-fp-math",
@@ -1746,6 +1749,12 @@
         "correctly-rounded-divide-sqrt-fp-math",
         llvm::toStringRef(CodeGenOpts.CorrectlyRoundedDivSqrt));
 
+    // TODO: Reciprocal estimate codegen options should apply to instructions?
+    std::vector<std::string> &Recips = getTarget().getTargetOpts().Reciprocals;
+    if (!Recips.empty())
+      FuncAttrs.addAttribute("mrecip",
+                             llvm::join(Recips.begin(), Recips.end(), ","));
+
     if (CodeGenOpts.StackRealignment)
       FuncAttrs.addAttribute("stackrealign");
     if (CodeGenOpts.Backchain)
Index: lib/CodeGen/BackendUtil.cpp
===================================================================
--- lib/CodeGen/BackendUtil.cpp
+++ lib/CodeGen/BackendUtil.cpp
@@ -529,9 +529,6 @@
 
   llvm::TargetOptions Options;
 
-  if (!TargetOpts.Reciprocals.empty())
-    Options.Reciprocals = TargetRecip(TargetOpts.Reciprocals);
-
   Options.ThreadModel =
     llvm::StringSwitch<llvm::ThreadModel::Model>(CodeGenOpts.ThreadModel)
       .Case("posix", llvm::ThreadModel::POSIX)


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