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nir/search: Don't match inexact expressions with exact subexpressions 

In the first pass of implementing exact handling, I made a mistake with
search-and-replace.  In particular, we only reallly handled exact/inexact
on the root of the tree.  Instead, we need to check every node in the tree
for an exact/inexact match.  As an example of this, consider the following
GLSL code

precise float a = b + c;
if (a < 0) {
   do_stuff();
}

In that case, only the add will be declared "exact" and an expression that
looks for "b + c < 0" will still match and replace it with "b < -c" which
may yield different results.  The solution is to simply bail if any of the
values are exact when matching an inexact expression.
This commit is contained in:
Jason Ekstrand 2016-03-28 11:12:33 -07:00
parent 6d658e9bd5
commit 035f66025b
1 changed files with 18 additions and 5 deletions
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23
src/compiler/nir/nir_search.c
View File

@ -28,6 +28,8 @@
#include "nir_search.h"
struct match_state {
bool inexact_match;
bool has_exact_alu;
unsigned variables_seen;
nir_alu_src variables[NIR_SEARCH_MAX_VARIABLES];
};
@ -239,7 +241,10 @@ match_expression(const nir_search_expression *expr, nir_alu_instr *instr,
return false;
assert(instr->dest.dest.is_ssa);
if (expr->inexact && instr->exact)
state->inexact_match = expr->inexact || state->inexact_match;
state->has_exact_alu = instr->exact || state->has_exact_alu;
if (state->inexact_match && state->has_exact_alu)
return false;
assert(!instr->dest.saturate);
@ -410,7 +415,7 @@ bitsize_tree_filter_down(bitsize_tree *tree, unsigned size)
static nir_alu_src
construct_value(const nir_search_value *value,
unsigned num_components, bitsize_tree *bitsize, bool exact,
unsigned num_components, bitsize_tree *bitsize,
struct match_state *state,
nir_instr *instr, void *mem_ctx)
{
@ -424,10 +429,16 @@ construct_value(const nir_search_value *value,
nir_alu_instr *alu = nir_alu_instr_create(mem_ctx, expr->opcode);
nir_ssa_dest_init(&alu->instr, &alu->dest.dest, num_components,
bitsize->dest_size, NULL);
alu->exact = exact;
alu->dest.write_mask = (1 << num_components) - 1;
alu->dest.saturate = false;
/* We have no way of knowing what values in a given search expression
* map to a particular replacement value. Therefore, if the
* expression we are replacing has any exact values, the entire
* replacement should be exact.
*/
alu->exact = state->has_exact_alu;
for (unsigned i = 0; i < nir_op_infos[expr->opcode].num_inputs; i++) {
/* If the source is an explicitly sized source, then we need to reset
* the number of components to match.
@ -436,7 +447,7 @@ construct_value(const nir_search_value *value,
num_components = nir_op_infos[alu->op].input_sizes[i];
alu->src[i] = construct_value(expr->srcs[i],
num_components, bitsize->srcs[i], exact,
num_components, bitsize->srcs[i],
state, instr, mem_ctx);
}
@ -546,6 +557,8 @@ nir_replace_instr(nir_alu_instr *instr, const nir_search_expression *search,
assert(instr->dest.dest.is_ssa);
struct match_state state;
state.inexact_match = false;
state.has_exact_alu = false;
state.variables_seen = 0;
if (!match_expression(search, instr, instr->dest.dest.ssa.num_components,
@ -569,7 +582,7 @@ nir_replace_instr(nir_alu_instr *instr, const nir_search_expression *search,
mov->src[0] = construct_value(replace,
instr->dest.dest.ssa.num_components, tree,
instr->exact, &state, &instr->instr, mem_ctx);
&state, &instr->instr, mem_ctx);
nir_instr_insert_before(&instr->instr, &mov->instr);
nir_ssa_def_rewrite_uses(&instr->dest.dest.ssa,