[Mesa-dev] [PATCH] gallivm: Make sure module has the correct data layout when pass manager runs

[Tom Stellard]

The datalayout for modules was purposely not being set in order to work around
the fact that the ExecutionEngine requires that the module's datalayout
matches the datalayout of the TargetMachine that the ExecutionEngine is
using.

When the pass manager runs on a module with no datalayout, it uses
the default datalayout which is little-endian.  This causes problems
on big-endian targets, because some optimizations that are legal on
little-endian or illegal on big-endian.

To resolve this, we set the datalayout prior to running the pass
manager, and then clear it before creating the ExectionEngine.

This patch fixes a lot of piglit tests on big-endian ppc64.

Cc: mesa-stable at lists.freedesktop.org
---
 src/gallium/auxiliary/gallivm/lp_bld_init.c | 34 +++++++++++++++--------------
 1 file changed, 18 insertions(+), 16 deletions(-)

diff --git a/src/gallium/auxiliary/gallivm/lp_bld_init.c b/src/gallium/auxiliary/gallivm/lp_bld_init.c
index ef2580e..9f1ade6 100644
--- a/src/gallium/auxiliary/gallivm/lp_bld_init.c
+++ b/src/gallium/auxiliary/gallivm/lp_bld_init.c
@@ -125,19 +125,6 @@ create_pass_manager(struct gallivm_state *gallivm)
    LLVMAddTargetData(gallivm->target, gallivm->passmgr);
 #endif
 
-   /* Setting the module's DataLayout to an empty string will cause the
-    * ExecutionEngine to copy to the DataLayout string from its target
-    * machine to the module.  As of LLVM 3.8 the module and the execution
-    * engine are required to have the same DataLayout.
-    *
-    * TODO: This is just a temporary work-around.  The correct solution is
-    * for gallivm_init_state() to create a TargetMachine and pull the
-    * DataLayout from there.  Currently, the TargetMachine used by llvmpipe
-    * is being implicitly created by the EngineBuilder in
-    * lp_build_create_jit_compiler_for_module()
-    */
-
-#if HAVE_LLVM < 0x0308
    {
       char *td_str;
       // New ones from the Module.
@@ -145,9 +132,6 @@ create_pass_manager(struct gallivm_state *gallivm)
       LLVMSetDataLayout(gallivm->module, td_str);
       free(td_str);
    }
-#else
-   LLVMSetDataLayout(gallivm->module, "");
-#endif
 
    if ((gallivm_debug & GALLIVM_DEBUG_NO_OPT) == 0) {
       /* These are the passes currently listed in llvm-c/Transforms/Scalar.h,
@@ -628,6 +612,24 @@ gallivm_compile_module(struct gallivm_state *gallivm)
    }
 
    if (use_mcjit) {
+      /* Setting the module's DataLayout to an empty string will cause the
+       * ExecutionEngine to copy to the DataLayout string from its target
+       * machine to the module.  As of LLVM 3.8 the module and the execution
+       * engine are required to have the same DataLayout.
+       *
+       * We must make sure we do this after running the optimization passes,
+       * because those passes need a correct datalayout string.  For example,
+       * if those optimization passes see an empty datalayout, they will assume
+       * this is a little endian target and will do optimizations that break big
+       * endian machines.
+       *
+       * TODO: This is just a temporary work-around.  The correct solution is
+       * for gallivm_init_state() to create a TargetMachine and pull the
+       * DataLayout from there.  Currently, the TargetMachine used by llvmpipe
+       * is being implicitly created by the EngineBuilder in
+       * lp_build_create_jit_compiler_for_module()
+       */
+      LLVMSetDataLayout(gallivm->module, "");
       assert(!gallivm->engine);
       if (!init_gallivm_engine(gallivm)) {
          assert(0);
-- 
2.9.3