Mesa (master): llvmpipe: work-around an LLVM bug

[Brian Paul]

Module: Mesa
Branch: master
Commit: a57e762c90b65f05a6e179b90c1d6fe5c80e977c
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=a57e762c90b65f05a6e179b90c1d6fe5c80e977c

Author: Brian Paul <brianp at vmware.com>
Date:   Fri Apr 16 13:34:28 2010 -0600

llvmpipe: work-around an LLVM bug

The blend combinations ZERO,DST_ALPHA and ZERO,INV_DST_ALPHA seem to
generate bad code which leads to a segfault.

---

 src/gallium/drivers/llvmpipe/lp_bld_blend_soa.c |   17 +++++++++++++++++
 1 files changed, 17 insertions(+), 0 deletions(-)

diff --git a/src/gallium/drivers/llvmpipe/lp_bld_blend_soa.c b/src/gallium/drivers/llvmpipe/lp_bld_blend_soa.c
index 39ea9ed..b7523eb 100644
--- a/src/gallium/drivers/llvmpipe/lp_bld_blend_soa.c
+++ b/src/gallium/drivers/llvmpipe/lp_bld_blend_soa.c
@@ -262,6 +262,23 @@ lp_build_blend_soa(LLVMBuilderRef builder,
                   bld.term[k][i] = bld.term[k][j];
                else
                   bld.term[k][i] = lp_build_mul(&bld.base, bld.factor[k][0][i], bld.factor[k][1][i]);
+
+               if (src_factor == PIPE_BLENDFACTOR_ZERO &&
+                   (dst_factor == PIPE_BLENDFACTOR_DST_ALPHA ||
+                    dst_factor == PIPE_BLENDFACTOR_INV_DST_ALPHA)) {
+                  /* XXX special case these combos to work around an apparent
+                   * bug in LLVM.
+                   * This hack disables the check for multiplication by zero
+                   * in lp_bld_mul().  When we optimize away the multiplication,
+                   * something goes wrong during code generation and we segfault
+                   * at runtime.
+                   */
+                  LLVMValueRef zeroSave = bld.base.zero;
+                  bld.base.zero = NULL;
+                  bld.term[k][i] = lp_build_mul(&bld.base, bld.factor[k][0][i],
+                                                bld.factor[k][1][i]);
+                  bld.base.zero = zeroSave;
+               }
             }
 
             /*