On 16/04/16 22:30, srol...@vmware.com wrote:
From: Roland Scheidegger <srol...@vmware.com>
llvm 3.7 sometimes simply miscompiles vector selects.
Reviewed-by: Jose Fonseca <jfons...@vmware.com>
See https://bugs.freedesktop.org/show_bug.cgi?id=94972
Great detective work.
I think you should make a LLVM test case out of the IR on that bug and
propose on llvm-commits, to guarantee it won't regress again. See
test/CodeGen/X86/vselect-avx.ll for example.
Jose
---
src/gallium/auxiliary/gallivm/lp_bld_logic.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/src/gallium/auxiliary/gallivm/lp_bld_logic.c
b/src/gallium/auxiliary/gallivm/lp_bld_logic.c
index 91f316c..620aece 100644
--- a/src/gallium/auxiliary/gallivm/lp_bld_logic.c
+++ b/src/gallium/auxiliary/gallivm/lp_bld_logic.c
@@ -315,14 +315,16 @@ lp_build_select(struct lp_build_context *bld,
mask = LLVMBuildTrunc(builder, mask, LLVMInt1TypeInContext(lc), "");
res = LLVMBuildSelect(builder, mask, a, b, "");
}
- else if (LLVMIsConstant(mask) ||
- LLVMGetInstructionOpcode(mask) == LLVMSExt) {
+ else if (!(HAVE_LLVM == 0x0307) &&
+ (LLVMIsConstant(mask) ||
+ LLVMGetInstructionOpcode(mask) == LLVMSExt)) {
/* Generate a vector select.
*
* Using vector selects should avoid emitting intrinsics hence avoid
- * hidering optimization passes, but vector selects weren't properly
+ * hindering optimization passes, but vector selects weren't properly
* supported yet for a long time, and LLVM will generate poor code when
* the mask is not the result of a comparison.
+ * Also, llvm 3.7 may miscompile them (bug 94972).
*/
/* Convert the mask to a vector of booleans.
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