Mesa (master): freedreno/ir3: don't allow negative const_offset

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Module: Mesa
Branch: master
Commit: c4dc877cb5df63a6a86013e32695f72c604625ad
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=c4dc877cb5df63a6a86013e32695f72c604625ad

Author: Rob Clark <robdclark at chromium.org>
Date:   Thu May  7 11:09:17 2020 -0700

freedreno/ir3: don't allow negative const_offset

Signed-off-by: Rob Clark <robdclark at chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4954>

---

 src/freedreno/ir3/ir3_nir_analyze_ubo_ranges.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/src/freedreno/ir3/ir3_nir_analyze_ubo_ranges.c b/src/freedreno/ir3/ir3_nir_analyze_ubo_ranges.c
index d2fe65cd0e3..d8a285073f1 100644
--- a/src/freedreno/ir3/ir3_nir_analyze_ubo_ranges.c
+++ b/src/freedreno/ir3/ir3_nir_analyze_ubo_ranges.c
@@ -143,7 +143,7 @@ gather_ubo_ranges(nir_shader *nir, nir_intrinsic_instr *instr,
  * with (ie. not requiring value range tracking)
  */
 static void
-handle_partial_const(nir_builder *b, nir_ssa_def **srcp, unsigned *offp)
+handle_partial_const(nir_builder *b, nir_ssa_def **srcp, int *offp)
 {
 	if ((*srcp)->parent_instr->type != nir_instr_type_alu)
 		return;
@@ -233,7 +233,7 @@ lower_ubo_load_to_uniform(nir_intrinsic_instr *instr, nir_builder *b,
 	}
 
 	nir_ssa_def *ubo_offset = nir_ssa_for_src(b, instr->src[1], 1);
-	unsigned const_offset = 0;
+	int const_offset = 0;
 
 	handle_partial_const(b, &ubo_offset, &const_offset);
 
@@ -262,9 +262,20 @@ lower_ubo_load_to_uniform(nir_intrinsic_instr *instr, nir_builder *b,
 		const_offset >>= 2;
 	}
 
-	const int range_offset = (range->offset - range->start) / 4;
+	const int range_offset = ((int)range->offset - (int)range->start) / 4;
 	const_offset += range_offset;
 
+	/* The range_offset could be negative, if if only part of the UBO
+	 * block is accessed, range->start can be greater than range->offset.
+	 * But we can't underflow const_offset.  If necessary we need to
+	 * insert nir instructions to compensate (which can hopefully be
+	 * optimized away)
+	 */
+	if (const_offset < 0) {
+		uniform_offset = nir_iadd_imm(b, uniform_offset, const_offset);
+		const_offset = 0;
+	}
+
 	nir_intrinsic_instr *uniform =
 		nir_intrinsic_instr_create(b->shader, nir_intrinsic_load_uniform);
 	uniform->num_components = instr->num_components;