[llvm-commits] [dragonegg] r140381 - in /dragonegg/trunk: README src/Backend.cpp

[Duncan Sands]

Author: baldrick
Date: Fri Sep 23 10:21:11 2011
New Revision: 140381

URL: http://llvm.org/viewvc/llvm-project?rev=140381&view=rev
Log:
When GCC optimizations are enabled, by default we were doing almost no LLVM
optimization (just simplifycfg+scalarrepl+earlycse).  While this is amusing,
experiments show that -O1 is a better choice.  So set things up so that is
what you get by default when running the GCC optimizers at -O3.  If anyone
wants more LLVM optimization, they can either run the GCC optimizers at -O4
or -O6 (which doesn't cause GCC to do any more optimization; instead it bumps
the level of LLVM optimization up to -O2 and -O3 respectively), or explicitly
ask for an LLVM optimization level using the option
-fplugin-arg-dragonegg-llvm-ir-optimize=level.

Modified:
    dragonegg/trunk/README
    dragonegg/trunk/src/Backend.cpp

Modified: dragonegg/trunk/README
URL: http://llvm.org/viewvc/llvm-project/dragonegg/trunk/README?rev=140381&r1=140380&r2=140381&view=diff
==============================================================================
--- dragonegg/trunk/README (original)
+++ dragonegg/trunk/README Fri Sep 23 10:21:11 2011
@@ -112,9 +112,9 @@
 
 -fplugin-arg-dragonegg-enable-gcc-optzns
   Run the GCC tree optimizers rather than the LLVM IR optimizers (normally all
-  GCC optimizations are disabled).  This disables the LLVM IR optimizers, except
-  for a small set of cleanup passes (to override this and run the usual set of
-  LLVM IR optimizers, use the -fplugin-arg-dragonegg-llvm-ir-optimize option).
+  GCC optimizations are disabled).  By default this severely reduces the amount
+  of LLVM IR optimization.  Use -O4 to -O6 to have LLVM optimize harder, or set
+  an explicit level using the -fplugin-arg-dragonegg-llvm-ir-optimize option.
 
 -fplugin-arg-dragonegg-save-gcc-output
   GCC assembler output is normally redirected to /dev/null so that it doesn't

Modified: dragonegg/trunk/src/Backend.cpp
URL: http://llvm.org/viewvc/llvm-project/dragonegg/trunk/src/Backend.cpp?rev=140381&r1=140380&r2=140381&view=diff
==============================================================================
--- dragonegg/trunk/src/Backend.cpp (original)
+++ dragonegg/trunk/src/Backend.cpp Fri Sep 23 10:21:11 2011
@@ -207,16 +207,39 @@
 /// PerFunctionOptLevel - The optimization level to be used by the per-function
 /// IR optimizers.
 static int PerFunctionOptLevel() {
-  return LLVMIROptimizeArg >= 0 ? LLVMIROptimizeArg : optimize;
+  // If the user supplied an LLVM optimization level then use it.
+  if (LLVMIROptimizeArg >= 0)
+    return LLVMIROptimizeArg;
+  // If the GCC optimizers were run then tone down the LLVM optimization level:
+  //   GCC | LLVM
+  //   ----------
+  //     0 |   0
+  //  >= 1 |   1 (per-function maximum)
+  if (EnableGCCOptimizations)
+    return optimize > 0;
+  // Otherwise use the GCC optimization level.
+  return optimize;
 }
 
 /// ModuleOptLevel - The optimization level to be used by the module level IR
 /// optimizers.
 static int ModuleOptLevel() {
+  // If the user supplied an LLVM optimization level then use it.
   if (LLVMIROptimizeArg >= 0)
     return LLVMIROptimizeArg;
+  // If the GCC optimizers were run then tone down the LLVM optimization level:
+  //   GCC | LLVM
+  //   ----------
+  //     0 |   0
+  //     1 |   0
+  //     2 |   1
+  //     3 |   1
+  //     4 |   2
+  //     5 |   2
+  //  >= 6 |   3 (per-module maximum)
   if (EnableGCCOptimizations)
-    return 0;
+    return optimize / 2;
+  // Otherwise use the GCC optimization level.
   return optimize;
 }