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gallivm: Workaround http://llvm.org/PR18600 

We have code generation paths that carry out swizzles of AoS vectors via
bitwise shifts, as these tend to generate more efficient code than
straightforward byte shuffles.  But when the input is a constant the
additional bitwise arithmetic operations somehow don't really get
constant propagated properly, evenutally causing assertion failure in
InstCombine pass.

Therefore avoid the bug by using the trivial shuffles for constant
inputs.

Although the sample LLVM IR can cause a crash with any LLVM version,
this was only seen in practice with LLVM 3.2.

Reviewed-by: Matthew McClure <mcclurem@vmware.com>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>
This commit is contained in:
José Fonseca 2014-01-24 14:25:46 +00:00
parent 37f1903e00
commit 2eddf91faf
1 changed files with 4 additions and 2 deletions
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6
src/gallium/auxiliary/gallivm/lp_bld_swizzle.c
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@ -180,7 +180,8 @@ lp_build_swizzle_scalar_aos(struct lp_build_context *bld,
/* XXX: SSE3 has PSHUFB which should be better than bitmasks, but forcing
* using shuffles here actually causes worst results. More investigation is
* needed. */
if (type.width >= 16) {
if (LLVMIsConstant(a) ||
type.width >= 16) {
/*
* Shuffle.
*/
@ -398,7 +399,8 @@ lp_build_swizzle_aos(struct lp_build_context *bld,
}
}
if (type.width >= 16) {
if (LLVMIsConstant(a) ||
type.width >= 16) {
/*
* Shuffle.
*/