Fix: Keep live ranges inside the program when a branch ends it.

src/RegisterAllocator.cpp

@@ -457,13 +457,17 @@ bool RegisterAllocator::processBranchState( BranchState* state, std::list<Token>
 
 			std::list<Token>::iterator target;
 
+			// the path runs up to the token after the branch, or to the branch
+			// itself when it ends the program
+			Token& after = (curr != end) ? *curr : token;
+
 			if( token.operand()->flags() & Operand::DYNAMIC )
 			{
 				if( !state->address( *branchDest, target, m_labels ) )
 					continue;
 
 				unsigned int targetLine = (*target).lineNumber();
-				unsigned int currentLine = (*curr).lineNumber();
+				unsigned int currentLine = after.lineNumber();
 				bool isBackwardBranch = targetLine < currentLine;
 
 				if( state->isBranchTaken( &*target ) )
@@ -490,7 +494,7 @@ bool RegisterAllocator::processBranchState( BranchState* state, std::list<Token>
 				BranchState* newState = new BranchState( *state );
 				assert( newState );
 
-				newState->pushTraces( &*curr, false );
+				newState->pushTraces( &after, false );
 				newState->pushTraces( &*target, true );
 				newState->setCurrent( target );
 
@@ -505,15 +509,15 @@ bool RegisterAllocator::processBranchState( BranchState* state, std::list<Token>
 				{
 					// Backward branch (loop back-edge) - extend live ranges to cover loop body
 					unsigned int targetLine = (*target).lineNumber();
-					unsigned int currentLine = (*curr).lineNumber();
+					unsigned int currentLine = after.lineNumber();
 					if( targetLine < currentLine )
 						state->extendLiveRanges( targetLine, currentLine );
 					break;
 				}
 
 				state->storeBranch( &*target );
 
-				state->pushTraces( &*curr, false );
+				state->pushTraces( &after, false );
 				state->pushTraces( &*target, true );
 
 				curr = target;

test/CMakeLists.txt

@@ -79,6 +79,7 @@ set(OPENVCL_TEST_SOURCES
     ${CMAKE_CURRENT_SOURCE_DIR}/integration/test_instruction_info_dump.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/integration/test_pairing.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/integration/test_literal_register_conflict.cpp
+    ${CMAKE_CURRENT_SOURCE_DIR}/integration/test_trailing_branch_ranges.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/integration/test_flag_latency.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/integration/test_emit_source.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/integration/test_continuation_lifetime.cpp

test/integration/test_trailing_branch_ranges.cpp

@@ -0,0 +1,65 @@
+// Regression test: a branch that ends the program keeps live ranges inside
+// the program.
+//
+// The register allocator ends a path's stretch of the program at the token
+// after a branch.  When the branch was the program's last token, as in
+// ps2gl's programs that loop back with `b` and have no --exit block, that
+// token was the end of the token list: dereferencing it read whatever lay
+// past the list, and the ranges of values live across the branch ended at
+// that number.
+
+#include "test_harness.h"
+#include "openvcl_runner.h"
+
+#include <cstdlib>
+#include <string>
+#include <vector>
+
+namespace
+{
+    // fA and iN are live across the b on the last line, line 11.
+    const char* kTrailingBranch =
+        "\t.init_vf_all\n"
+        "\t.init_vi_all\n"
+        "\t.syntax new\n"
+        "\t--enter\n"
+        "\t--endenter\n"
+        "\tlq fA, 0(vi00)\n"
+        "\tiaddiu iN, vi00, 1\n"
+        "lLoop:\n"
+        "\tsq fA, 1(iN)\n"
+        "\tiaddiu iN, iN, 1\n"
+        "\tb lLoop\n";
+
+    const unsigned long kLastLine = 11;
+
+    // The ends of the [start-stop] ranges --show-reg-alloc prints.
+    std::vector<unsigned long> rangeEnds(const std::string& report)
+    {
+        std::vector<unsigned long> result;
+        std::string::size_type open = report.find('[');
+        while (open != std::string::npos)
+        {
+            const std::string::size_type dash = report.find('-', open);
+            const std::string::size_type close = report.find(']', open);
+            if (dash != std::string::npos && close != std::string::npos && dash < close
+                && report.find_first_not_of("0123456789", open + 1) == dash)
+                result.push_back(std::strtoul(report.c_str() + dash + 1, NULL, 10));
+            open = report.find('[', open + 1);
+        }
+        return result;
+    }
+}
+
+TEST_CASE("openvcl: values live across a branch that ends the program keep ranges inside it")
+{
+    std::vector<std::string> args;
+    args.push_back("--show-reg-alloc");
+    ::test::RunResult result = ::test::run_openvcl(args, kTrailingBranch);
+    REQUIRE(result.exit_code == 0);
+
+    const std::vector<unsigned long> ends = rangeEnds(result.stderr_data);
+    REQUIRE(!ends.empty());
+    for (unsigned int i = 0; i < ends.size(); ++i)
+        CHECK(ends[i] <= kLastLine);
+}