[FuncSpec] Handle ssa_copy intrinsic calls in InstCostVisitor

Look through ssa_copy intrinsic calls when computing codesize bonus for
a specialization.

Also remove redundant logic to skip computing codesize bonus for
ssa_copy intrinsics, now these are considered zero-cost by TTI
(in PR#75294).

Author: hazzlim

llvm/lib/Transforms/IPO/FunctionSpecialization.cpp

@@ -120,10 +120,6 @@ Cost InstCostVisitor::estimateBasicBlocks(
       continue;
 
     for (Instruction &I : *BB) {
-      // Disregard SSA copies.
-      if (auto *II = dyn_cast<IntrinsicInst>(&I))
-        if (II->getIntrinsicID() == Intrinsic::ssa_copy)
-          continue;
       // If it's a known constant we have already accounted for it.
       if (KnownConstants.contains(&I))
         continue;
@@ -402,6 +398,14 @@ Constant *InstCostVisitor::visitFreezeInst(FreezeInst &I) {
 }
 
 Constant *InstCostVisitor::visitCallBase(CallBase &I) {
+  assert(LastVisited != KnownConstants.end() && "Invalid iterator!");
+
+  // Look through calls to ssa_copy intrinsics.
+  if (auto *II = dyn_cast<IntrinsicInst>(&I);
+      II && II->getIntrinsicID() == Intrinsic::ssa_copy) {
+    return LastVisited->second;
+  }
+
   Function *F = I.getCalledFunction();
   if (!F || !canConstantFoldCallTo(&I, F))
     return nullptr;

llvm/test/Transforms/FunctionSpecialization/ssa-copy.ll

@@ -8,8 +8,6 @@
 ; Verify that we are able to estimate the codesize savings by looking through
 ; calls to ssa_copy intrinsics, which are inserted by PredicateInfo when IPSCCP
 ; is run prior to FunctionSpecialization.
-; FIXME: We should be able to specialize this, but we currently do not handle
-; FIXME: llvm.ssa.copy calls in InstCostVisitor.
 define i32 @main() {
 entry:
   %res = call i32 @test_ssa_copy(i32 0)
@@ -43,10 +41,10 @@ exit4:
   ret i32 999
 }
 
-; CHECK-LABEL: define range(i32 1, 0) i32 @main() {
+; CHECK-LABEL: define i32 @main() {
 ; CHECK-NEXT:  [[ENTRY:.*:]]
-; CHECK-NEXT:    [[RES:%.*]] = call i32 @test_ssa_copy(i32 0)
-; CHECK-NEXT:    ret i32 [[RES]]
+; CHECK-NEXT:    [[RES:%.*]] = call i32 @test_ssa_copy.specialized.1(i32 0)
+; CHECK-NEXT:    ret i32 999
 ;
 ;
 ; CHECK-LABEL: define range(i32 1, 0) i32 @test_ssa_copy(
@@ -65,3 +63,17 @@ exit4:
 ; CHECK:       [[EXIT4]]:
 ; CHECK-NEXT:    ret i32 999
 ;
+;
+; CHECK-LABEL: define internal i32 @test_ssa_copy.specialized.1(
+; CHECK-SAME: i32 [[X:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    br label %[[BLOCK1:.*]]
+; CHECK:       [[BLOCK1]]:
+; CHECK-NEXT:    br label %[[BLOCK2:.*]]
+; CHECK:       [[BLOCK2]]:
+; CHECK-NEXT:    br label %[[BLOCK3:.*]]
+; CHECK:       [[BLOCK3]]:
+; CHECK-NEXT:    br label %[[EXIT4:.*]]
+; CHECK:       [[EXIT4]]:
+; CHECK-NEXT:    ret i32 poison
+;