Mesa (master): nv50/ir: only stick one preret per function

[Ilia Mirkin]

Module: Mesa
Branch: master
Commit: ec05331a7b0d6b6bb84fa6452fbba4bf5dc25f83
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=ec05331a7b0d6b6bb84fa6452fbba4bf5dc25f83

Author: Ilia Mirkin <imirkin at alum.mit.edu>
Date:   Sun Oct  9 00:09:54 2016 -0400

nv50/ir: only stick one preret per function

A function with multiple returns would have had multiple preret settings
at the top of the function. While this is unlikely to have caused issues
since we don't use functions in earnest, it could have in some cases
overflowed the call stack, in case a function had a lot of early
returns.

Signed-off-by: Ilia Mirkin <imirkin at alum.mit.edu>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset at gmail.com>

---

 src/gallium/drivers/nouveau/codegen/nv50_ir_from_tgsi.cpp | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/src/gallium/drivers/nouveau/codegen/nv50_ir_from_tgsi.cpp b/src/gallium/drivers/nouveau/codegen/nv50_ir_from_tgsi.cpp
index 7dff08a..db03281 100644
--- a/src/gallium/drivers/nouveau/codegen/nv50_ir_from_tgsi.cpp
+++ b/src/gallium/drivers/nouveau/codegen/nv50_ir_from_tgsi.cpp
@@ -3465,10 +3465,13 @@ Converter::handleInstruction(const struct tgsi_full_instruction *insn)
       if (!isEndOfSubroutine(ip + 1)) {
          // insert a PRERET at the entry if this is an early return
          // (only needed for sharing code in the epilogue)
-         BasicBlock *pos = getBB();
-         setPosition(BasicBlock::get(func->cfg.getRoot()), false);
-         mkFlow(OP_PRERET, leave, CC_ALWAYS, NULL)->fixed = 1;
-         setPosition(pos, true);
+         BasicBlock *root = BasicBlock::get(func->cfg.getRoot());
+         if (root->getEntry() == NULL || root->getEntry()->op != OP_PRERET) {
+            BasicBlock *pos = getBB();
+            setPosition(root, false);
+            mkFlow(OP_PRERET, leave, CC_ALWAYS, NULL)->fixed = 1;
+            setPosition(pos, true);
+         }
       }
       mkFlow(OP_RET, NULL, CC_ALWAYS, NULL)->fixed = 1;
       bb->cfg.attach(&leave->cfg, Graph::Edge::CROSS);