Revert "Revert "As a follow-up to my initial mail to llvm-dev here's a first pass at the O1 described there.""

This reapplies: 8ff85ed905a7306977d07a5cd67ab4d5a56fafb4

Original commit message:

As a follow-up to my initial mail to llvm-dev here's a first pass at the O1 described there.

This change doesn't include any change to move from selection dag to fast isel
and that will come with other numbers that should help inform that decision.
There also haven't been any real debuggability studies with this pipeline yet,
this is just the initial start done so that people could see it and we could start
tweaking after.

Test updates: Outside of the newpm tests most of the updates are coming from either
optimization passes not run anymore (and without a compelling argument at the moment)
that were largely used for canonicalization in clang.

Original post:

http://lists.llvm.org/pipermail/llvm-dev/2019-April/131494.html

Tags: #llvm
Differential Revision: https://reviews.llvm.org/D65410

This reverts commit c9ddb02659e3ece7a0d9d6b4dac7ceea4ae46e6d.

1 files changed, 30 insertions, 16 deletions

diff --git a/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp b/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
index 5314a8219b1..81424229c3b 100644
--- a/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
+++ b/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
@@ -320,19 +320,26 @@ void PassManagerBuilder::addFunctionSimplificationPasses(
     legacy::PassManagerBase &MPM) {
   // Start of function pass.
   // Break up aggregate allocas, using SSAUpdater.
+  assert(OptLevel >= 1 && "Calling function optimizer with no optimization level!");
   MPM.add(createSROAPass());
   MPM.add(createEarlyCSEPass(true /* Enable mem-ssa. */)); // Catch trivial redundancies
-  if (EnableGVNHoist)
-    MPM.add(createGVNHoistPass());
-  if (EnableGVNSink) {
-    MPM.add(createGVNSinkPass());
-    MPM.add(createCFGSimplificationPass());
+
+  if (OptLevel > 1) {
+    if (EnableGVNHoist)
+      MPM.add(createGVNHoistPass());
+    if (EnableGVNSink) {
+      MPM.add(createGVNSinkPass());
+      MPM.add(createCFGSimplificationPass());
+    }
   }
 
-  // Speculative execution if the target has divergent branches; otherwise nop.
-  MPM.add(createSpeculativeExecutionIfHasBranchDivergencePass());
-  MPM.add(createJumpThreadingPass());         // Thread jumps.
-  MPM.add(createCorrelatedValuePropagationPass()); // Propagate conditionals
+  if (OptLevel > 1) {
+    // Speculative execution if the target has divergent branches; otherwise nop.
+    MPM.add(createSpeculativeExecutionIfHasBranchDivergencePass());
+
+    MPM.add(createJumpThreadingPass());         // Thread jumps.
+    MPM.add(createCorrelatedValuePropagationPass()); // Propagate conditionals
+  }
   MPM.add(createCFGSimplificationPass());     // Merge & remove BBs
   // Combine silly seq's
   if (OptLevel > 2)
@@ -346,8 +353,10 @@ void PassManagerBuilder::addFunctionSimplificationPasses(
   if (SizeLevel == 0)
     MPM.add(createPGOMemOPSizeOptLegacyPass());
 
-  MPM.add(createTailCallEliminationPass()); // Eliminate tail calls
-  MPM.add(createCFGSimplificationPass());     // Merge & remove BBs
+  // TODO: Investigate the cost/benefit of tail call elimination on debugging.
+  if (OptLevel > 1)
+    MPM.add(createTailCallEliminationPass()); // Eliminate tail calls
+  MPM.add(createCFGSimplificationPass());      // Merge & remove BBs
   MPM.add(createReassociatePass());           // Reassociate expressions
 
   // Begin the loop pass pipeline.
@@ -360,6 +369,7 @@ void PassManagerBuilder::addFunctionSimplificationPasses(
   }
   // Rotate Loop - disable header duplication at -Oz
   MPM.add(createLoopRotatePass(SizeLevel == 2 ? 0 : -1));
+  // TODO: Investigate promotion cap for O1.
   MPM.add(createLICMPass(LicmMssaOptCap, LicmMssaNoAccForPromotionCap));
   if (EnableSimpleLoopUnswitch)
     MPM.add(createSimpleLoopUnswitchLegacyPass());
@@ -402,16 +412,19 @@ void PassManagerBuilder::addFunctionSimplificationPasses(
   // opened up by them.
   addInstructionCombiningPass(MPM);
   addExtensionsToPM(EP_Peephole, MPM);
-  MPM.add(createJumpThreadingPass());         // Thread jumps
-  MPM.add(createCorrelatedValuePropagationPass());
-  MPM.add(createDeadStoreEliminationPass());  // Delete dead stores
-  MPM.add(createLICMPass(LicmMssaOptCap, LicmMssaNoAccForPromotionCap));
+  if (OptLevel > 1) {
+    MPM.add(createJumpThreadingPass());         // Thread jumps
+    MPM.add(createCorrelatedValuePropagationPass());
+    MPM.add(createDeadStoreEliminationPass());  // Delete dead stores
+    MPM.add(createLICMPass(LicmMssaOptCap, LicmMssaNoAccForPromotionCap));
+  }
 
   addExtensionsToPM(EP_ScalarOptimizerLate, MPM);
 
   if (RerollLoops)
     MPM.add(createLoopRerollPass());
 
+  // TODO: Investigate if this is too expensive at O1.
   MPM.add(createAggressiveDCEPass());         // Delete dead instructions
   MPM.add(createCFGSimplificationPass()); // Merge & remove BBs
   // Clean up after everything.
@@ -899,7 +912,8 @@ void PassManagerBuilder::addLTOOptimizationPasses(legacy::PassManagerBase &PM) {
 
   // LTO provides additional opportunities for tailcall elimination due to
   // link-time inlining, and visibility of nocapture attribute.
-  PM.add(createTailCallEliminationPass());
+  if (OptLevel > 1)
+    PM.add(createTailCallEliminationPass());
 
   // Infer attributes on declarations, call sites, arguments, etc.
   PM.add(createPostOrderFunctionAttrsLegacyPass()); // Add nocapture.