[JumpThreading] Consider freeze as a zero-cost instruction

[aqjune]

Summary

This is a simple patch that makes freeze as a zero-cost instruction, as bitcast already is.

[aqjune]

Minor fix

[efriedma]

Can we combine all the thread-two-bbs tests into one file, instead of keeping them in separate numbered files?

llvm/test/Transforms/JumpThreading/thread-two-bbs7.ll

9 ↗

(On Diff #282200)

Please add a comment explaining what this is testing.

[aqjune]

I merged the tests to a single file (https://github.com/llvm/llvm-project/commit/1ea84653378132091b5b6d31d4f6bf3ec7da7b56 ).
Two tests required targets that are different from x86_64-unknown-linux-gnu , so they are left unmerged.

[aqjune]

Update test

[aqjune]

Minor fix

[efriedma]

LGTM

llvm/lib/Transforms/Scalar/JumpThreading.cpp

for (; &*I != StopAt; ++I) {
 
     // Debugger intrinsics don't incur code size.
     if (isa<DbgInfoIntrinsic>(I)) continue;
 
     // If this is a pointer->pointer bitcast, it is free.
     if (isa<BitCastInst>(I) && I->getType()->isPointerTy())
       continue;
 
+    // Freeze instruction is free, too.
+    if (isa<FreezeInst>(I))
+      continue;
+
     // Bail out if this instruction gives back a token type, it is not possible
     // to duplicate it if it is used outside this BB.
     if (I->getType()->isTokenTy() && I->isUsedOutsideOfBlock(BB))
       return ~0U;
 
     // All other instructions count for at least one unit.
     ++Size;
 

llvm/test/Transforms/JumpThreading/thread-two-bbs-threshold.ll

 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt < %s -jump-threading -jump-threading-threshold=3 -S -verify | FileCheck %s
 
 target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 
 @a = global i32 0, align 4
 
+; Show that freeze is not counted when comparing the cost with the threshold
 define void @foo(i32 %cond1, i32 %cond2) {
 ; CHECK-LABEL: @foo(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[TOBOOL:%.*]] = icmp eq i32 [[COND1:%.*]], 0
-; CHECK-NEXT:    br i1 [[TOBOOL]], label [[BB_COND2:%.*]], label [[BB_F1:%.*]]
-; CHECK:       bb.f1:
-; CHECK-NEXT:    call void @f1()
-; CHECK-NEXT:    br label [[BB_COND2]]
+; CHECK-NEXT:    br i1 [[TOBOOL]], label [[BB_COND2_THREAD:%.*]], label [[BB_COND2:%.*]]
 ; CHECK:       bb.cond2:
-; CHECK-NEXT:    [[PTR:%.*]] = phi i32* [ null, [[BB_F1]] ], [ @a, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    call void @f1()
 ; CHECK-NEXT:    [[COND2_FR:%.*]] = freeze i32 [[COND2:%.*]]
 ; CHECK-NEXT:    [[X:%.*]] = add i32 [[COND2_FR]], 1
 ; CHECK-NEXT:    [[TOBOOL1:%.*]] = icmp eq i32 [[X]], 0
-; CHECK-NEXT:    br i1 [[TOBOOL1]], label [[BB_FILE:%.*]], label [[BB_F2:%.*]]
+; CHECK-NEXT:    br i1 [[TOBOOL1]], label [[BB_F4:%.*]], label [[BB_F2:%.*]]
+; CHECK:       bb.cond2.thread:
+; CHECK-NEXT:    [[COND2_FR2:%.*]] = freeze i32 [[COND2]]
+; CHECK-NEXT:    [[X3:%.*]] = add i32 [[COND2_FR2]], 1
+; CHECK-NEXT:    [[TOBOOL14:%.*]] = icmp eq i32 [[X3]], 0
+; CHECK-NEXT:    br i1 [[TOBOOL14]], label [[BB_F3:%.*]], label [[BB_F2]]
 ; CHECK:       bb.f2:
 ; CHECK-NEXT:    call void @f2()
 ; CHECK-NEXT:    br label [[EXIT:%.*]]
-; CHECK:       bb.file:
-; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32* [[PTR]], null
-; CHECK-NEXT:    br i1 [[CMP]], label [[BB_F4:%.*]], label [[BB_F3:%.*]]
 ; CHECK:       bb.f3:
 ; CHECK-NEXT:    call void @f3()
 ; CHECK-NEXT:    br label [[EXIT]]
 ; CHECK:       bb.f4:
+; CHECK-NEXT:    [[PTR5:%.*]] = phi i32* [ null, [[BB_COND2]] ]
 ; CHECK-NEXT:    call void @f4()
 ; CHECK-NEXT:    br label [[EXIT]]
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret void
 ;
 entry:
   %tobool = icmp eq i32 %cond1, 0
   br i1 %tobool, label %bb.cond2, label %bb.f1