[CodeGenPrepare] Use MapVector to stabilize iteration order

DenseMap iteration order is not guaranteed to be deterministic.

Without the change,
llvm/test/Transforms/CodeGenPrepare/X86/statepoint-relocate.ll would
fail when `combineHashValue` changes (llvm#95970).

Fixes: dba7329

Author: MaskRay

llvm/lib/CodeGen/CodeGenPrepare.cpp

@@ -1194,12 +1194,12 @@ void CodeGenPrepare::eliminateMostlyEmptyBlock(BasicBlock *BB) {
 // derived pointer relocation instructions given a vector of all relocate calls
 static void computeBaseDerivedRelocateMap(
     const SmallVectorImpl<GCRelocateInst *> &AllRelocateCalls,
-    DenseMap<GCRelocateInst *, SmallVector<GCRelocateInst *, 2>>
+    MapVector<GCRelocateInst *, SmallVector<GCRelocateInst *, 0>>
         &RelocateInstMap) {
   // Collect information in two maps: one primarily for locating the base object
   // while filling the second map; the second map is the final structure holding
   // a mapping between Base and corresponding Derived relocate calls
-  DenseMap<std::pair<unsigned, unsigned>, GCRelocateInst *> RelocateIdxMap;
+  MapVector<std::pair<unsigned, unsigned>, GCRelocateInst *> RelocateIdxMap;
   for (auto *ThisRelocate : AllRelocateCalls) {
     auto K = std::make_pair(ThisRelocate->getBasePtrIndex(),
                             ThisRelocate->getDerivedPtrIndex());
@@ -1375,7 +1375,7 @@ bool CodeGenPrepare::simplifyOffsetableRelocate(GCStatepointInst &I) {
 
   // RelocateInstMap is a mapping from the base relocate instruction to the
   // corresponding derived relocate instructions
-  DenseMap<GCRelocateInst *, SmallVector<GCRelocateInst *, 2>> RelocateInstMap;
+  MapVector<GCRelocateInst *, SmallVector<GCRelocateInst *, 0>> RelocateInstMap;
   computeBaseDerivedRelocateMap(AllRelocateCalls, RelocateInstMap);
   if (RelocateInstMap.empty())
     return false;

llvm/test/Transforms/CodeGenPrepare/X86/statepoint-relocate.ll

@@ -18,10 +18,11 @@ entry:
 }
 
 define i32 @test_sor_two_derived(ptr addrspace(1) %base) gc "statepoint-example" {
+; CHECK-LABEL: @test_sor_two_derived(
 ; CHECK: getelementptr i32, ptr addrspace(1) %base, i32 15
 ; CHECK: getelementptr i32, ptr addrspace(1) %base, i32 12
-; CHECK: getelementptr i32, ptr addrspace(1) %base-new, i32 12
 ; CHECK: getelementptr i32, ptr addrspace(1) %base-new, i32 15
+; CHECK: getelementptr i32, ptr addrspace(1) %base-new, i32 12
 entry:
        %ptr = getelementptr i32, ptr addrspace(1) %base, i32 15
        %ptr2 = getelementptr i32, ptr addrspace(1) %base, i32 12
@@ -34,6 +35,7 @@ entry:
 }
 
 define i32 @test_sor_ooo(ptr addrspace(1) %base) gc "statepoint-example" {
+; CHECK-LABEL: @test_sor_ooo(
 ; CHECK: getelementptr i32, ptr addrspace(1) %base, i32 15
 ; CHECK: getelementptr i32, ptr addrspace(1) %base-new, i32 15
 entry: