[Mesa-dev] [PATCH] mesa/st/glsl_to_tgsi: Properly resolve life times for simple if/else + use constructs

[Gert Wollny]

In constructs like 

  while (foo)  {
    ...
    if (a) {
       ...
       if (b)
         foo = ...
       else
         foo = ...
       x = foo;
       ...
    }
     ...
  }

currently the live range estimation extends the live range of t unnecessarily 
to the whole loop because it was not detected that t is only read in the 
"if (a)" scope that encloses the "if (b)/else" constructs where t is written 
in both branches. 

This patch corrects the minimal live range estimation and adds an according 
unit test for this case.

Signed-off-by: Gert Wollny <gw.fossdev at gmail.com>
---
 .../state_tracker/st_glsl_to_tgsi_temprename.cpp   | 14 +++++++++++++
 .../tests/test_glsl_to_tgsi_lifetime.cpp           | 23 ++++++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/src/mesa/state_tracker/st_glsl_to_tgsi_temprename.cpp b/src/mesa/state_tracker/st_glsl_to_tgsi_temprename.cpp
index 6921a643b7..047bd9c7e1 100644
--- a/src/mesa/state_tracker/st_glsl_to_tgsi_temprename.cpp
+++ b/src/mesa/state_tracker/st_glsl_to_tgsi_temprename.cpp
@@ -741,6 +741,20 @@ void temp_comp_access::record_else_write(const prog_scope& scope)
          } else {
             current_unpaired_if_write_scope = nullptr;
          }
+         /* Promote the first write scope to the enclosing scope because the
+          * current IF/ELSE pair is now irrelevant for the analysis. This is
+          * needed to obtain the minimum live range for t in constructs like:
+          * {
+          *    var t;
+          *    if (a)
+          *      t = ...
+          *    else
+          *      t = ...
+          *    x = t;
+          *    ...
+          * }
+          */
+         first_write_scope = scope.parent();
 
          /* If some parent is IF/ELSE and in a loop then propagate the
           * write to that scope. Otherwise the write is unconditional
diff --git a/src/mesa/state_tracker/tests/test_glsl_to_tgsi_lifetime.cpp b/src/mesa/state_tracker/tests/test_glsl_to_tgsi_lifetime.cpp
index acebfb8293..464e46e44b 100644
--- a/src/mesa/state_tracker/tests/test_glsl_to_tgsi_lifetime.cpp
+++ b/src/mesa/state_tracker/tests/test_glsl_to_tgsi_lifetime.cpp
@@ -794,6 +794,29 @@ TEST_F(LifetimeEvaluatorExactTest, WriteInIfElseBranchSecondIfInLoop)
    run (code, temp_lt_expect({{-1,-1}, {2,9}}));
 }
 
+/*
+  Test for write in IF and ELSE and read in enclosing IF in loop.
+*/
+
+TEST_F(LifetimeEvaluatorExactTest, DeeplyNestedinLoop)
+{
+   const vector<FakeCodeline> code = {
+      { TGSI_OPCODE_BGNLOOP },
+      {   TGSI_OPCODE_UIF, {}, {in0}, {}},
+      {     TGSI_OPCODE_FSEQ, {1}, {in1,in2}, {}},
+      {     TGSI_OPCODE_UIF, {}, {1}, {}},
+      {       TGSI_OPCODE_MOV, {2}, {in1}, {}},
+      {     TGSI_OPCODE_ELSE },
+      {       TGSI_OPCODE_MOV, {2}, {in2}, {}},
+      {     TGSI_OPCODE_ENDIF },
+      {     TGSI_OPCODE_MOV, {3}, {2}, {}},
+      {   TGSI_OPCODE_ENDIF },
+      {   TGSI_OPCODE_ADD, {out0}, {3, in1}, {}},
+      { TGSI_OPCODE_ENDLOOP }
+   };
+   run (code, temp_lt_expect({{-1,-1}, {2,3}, {4, 8}, {0,11}}));
+}
+
 /** Regression test for bug #104803,
  *  Read and write in if/else path outside loop and later read in conditional
  *  within a loop. The first write is to be considered the dominant write.
-- 
2.16.1