Remove redundant iterations from inliner passes (#6639)

Implemented in both the exhaustive/opaque inliner even though it appears
the opaque one is not fully functional.

In my benchmark tests I found it reduced the time needed to run the
exhaustive pass by 50% on average with the shaders I was testing with.

Also fixes two bugs in the opaque inliner. One is from not updating the
parent of each new block and the other for debug. These could be split
into another PR if desired but it's still pretty small overall.

---------

Co-authored-by: Steven Perron <[email protected]>

Author: Jmangles

source/opt/inline_exhaustive_pass.cpp

@@ -16,6 +16,7 @@
 
 #include "source/opt/inline_exhaustive_pass.h"
 
+#include <iterator>
 #include <utility>
 
 namespace spvtools {
@@ -27,6 +28,10 @@ Pass::Status InlineExhaustivePass::InlineExhaustive(Function* func) {
   for (auto bi = func->begin(); bi != func->end(); ++bi) {
     for (auto ii = bi->begin(); ii != bi->end();) {
       if (IsInlinableFunctionCall(&*ii)) {
+        // Save instruction before the call to avoid redundant re-scanning.
+        Instruction* prev_inst =
+            (ii == bi->begin()) ? nullptr : &*std::prev(ii);
+
         // Inline call.
         std::vector<std::unique_ptr<BasicBlock>> newBlocks;
         std::vector<std::unique_ptr<Instruction>> newVars;
@@ -47,8 +52,8 @@ Pass::Status InlineExhaustivePass::InlineExhaustive(Function* func) {
         // Insert new function variables.
         if (newVars.size() > 0)
           func->begin()->begin().InsertBefore(std::move(newVars));
-        // Restart inlining at beginning of calling block.
-        ii = bi->begin();
+        // Restart inlining at the first instruction of the inlined code.
+        ii = prev_inst ? ++InstructionList::iterator(prev_inst) : bi->begin();
         modified = true;
       } else {
         ++ii;

source/opt/inline_opaque_pass.cpp

@@ -16,6 +16,7 @@
 
 #include "source/opt/inline_opaque_pass.h"
 
+#include <iterator>
 #include <utility>
 
 namespace spvtools {
@@ -67,6 +68,10 @@ Pass::Status InlineOpaquePass::InlineOpaque(Function* func) {
   for (auto bi = func->begin(); bi != func->end(); ++bi) {
     for (auto ii = bi->begin(); ii != bi->end();) {
       if (IsInlinableFunctionCall(&*ii) && HasOpaqueArgsOrReturn(&*ii)) {
+        // Save instruction before the call to avoid redundant re-scanning.
+        Instruction* prev_inst =
+            (ii == bi->begin()) ? nullptr : &*std::prev(ii);
+
         // Inline call.
         std::vector<std::unique_ptr<BasicBlock>> newBlocks;
         std::vector<std::unique_ptr<Instruction>> newVars;
@@ -79,18 +84,27 @@ Pass::Status InlineOpaquePass::InlineOpaque(Function* func) {
         if (newBlocks.size() > 1) UpdateSucceedingPhis(newBlocks);
         // Replace old calling block with new block(s).
         bi = bi.Erase();
+
+        for (auto& bb : newBlocks) {
+          bb->SetParent(func);
+        }
         bi = bi.InsertBefore(&newBlocks);
         // Insert new function variables.
         if (newVars.size() > 0)
           func->begin()->begin().InsertBefore(std::move(newVars));
-        // Restart inlining at beginning of calling block.
-        ii = bi->begin();
+        // Restart inlining at the first instruction of the inlined code.
+        ii = prev_inst ? ++InstructionList::iterator(prev_inst) : bi->begin();
         modified = true;
       } else {
         ++ii;
       }
     }
   }
+
+  if (modified) {
+    FixDebugDeclares(func);
+  }
+
   return (modified ? Status::SuccessWithChange : Status::SuccessWithoutChange);
 }