Fix uses of uninitialized data (#46965)

* Fix uses of uninitialized data

Fixes #46961

* Fix typo

* Formatting

src/coreclr/jit/codegenarmarch.cpp

@@ -473,8 +473,10 @@ void CodeGen::genCodeForTreeNode(GenTree* treeNode)
         case GT_PINVOKE_PROLOG:
             noway_assert(((gcInfo.gcRegGCrefSetCur | gcInfo.gcRegByrefSetCur) & ~fullIntArgRegMask()) == 0);
 
+#ifdef PSEUDORANDOM_NOP_INSERTION
             // the runtime side requires the codegen here to be consistent
             emit->emitDisableRandomNops();
+#endif // PSEUDORANDOM_NOP_INSERTION
             break;
 
         case GT_LABEL:

src/coreclr/jit/codegenxarch.cpp

@@ -1793,8 +1793,10 @@ void CodeGen::genCodeForTreeNode(GenTree* treeNode)
         case GT_PINVOKE_PROLOG:
             noway_assert(((gcInfo.gcRegGCrefSetCur | gcInfo.gcRegByrefSetCur) & ~fullIntArgRegMask()) == 0);
 
+#ifdef PSEUDORANDOM_NOP_INSERTION
             // the runtime side requires the codegen here to be consistent
             emit->emitDisableRandomNops();
+#endif // PSEUDORANDOM_NOP_INSERTION
             break;
 
         case GT_LABEL:

src/coreclr/jit/emit.h

@@ -1846,10 +1846,13 @@ class emitter
 
     unsigned emitNxtIGnum;
 
+#ifdef PSEUDORANDOM_NOP_INSERTION
+
     // random nop insertion to break up nop sleds
     unsigned emitNextNop;
     bool     emitRandomNops;
-    void     emitEnableRandomNops()
+
+    void emitEnableRandomNops()
     {
         emitRandomNops = true;
     }
@@ -1858,6 +1861,8 @@ class emitter
         emitRandomNops = false;
     }
 
+#endif // PSEUDORANDOM_NOP_INSERTION
+
     insGroup* emitAllocAndLinkIG();
     insGroup* emitAllocIG();
     void emitInitIG(insGroup* ig);

src/coreclr/jit/flowgraph.cpp

@@ -9237,18 +9237,19 @@ class MergedReturns
             // Need to check both for matching const val and for genReturnBB
             // because genReturnBB is used for non-constant returns and its
             // corresponding entry in the returnConstants array is garbage.
-            if (returnConstants[i] == constVal)
-            {
-                BasicBlock* returnBlock = returnBlocks[i];
+            // Check the returnBlocks[] first, so we don't access an uninitialized
+            // returnConstants[] value (which some tools like valgrind will
+            // complain about).
 
-                if (returnBlock == comp->genReturnBB)
-                {
-                    // This is the block used for non-constant returns, so
-                    // its returnConstants entry is just garbage; don't be
-                    // fooled.
-                    continue;
-                }
+            BasicBlock* returnBlock = returnBlocks[i];
 
+            if (returnBlock == comp->genReturnBB)
+            {
+                continue;
+            }
+
+            if (returnConstants[i] == constVal)
+            {
                 *index = i;
                 return returnBlock;
             }

src/coreclr/jit/instr.cpp

@@ -193,6 +193,7 @@ void CodeGen::instGen(instruction ins)
     GetEmitter()->emitIns(ins);
 
 #ifdef TARGET_XARCH
+#ifdef PSEUDORANDOM_NOP_INSERTION
     // A workaround necessitated by limitations of emitter
     // if we are scheduled to insert a nop here, we have to delay it
     // hopefully we have not missed any other prefix instructions or places
@@ -201,6 +202,7 @@ void CodeGen::instGen(instruction ins)
     {
         GetEmitter()->emitNextNop = 1;
     }
+#endif // PSEUDORANDOM_NOP_INSERTION
 #endif
 }
 

src/coreclr/jit/lsra.cpp

@@ -716,9 +716,10 @@ LinearScan::LinearScan(Compiler* theCompiler)
     , refPositions(theCompiler->getAllocator(CMK_LSRA_RefPosition))
     , listNodePool(theCompiler)
 {
+    firstColdLoc = MaxLocation;
+
 #ifdef DEBUG
     maxNodeLocation   = 0;
-    firstColdLoc      = MaxLocation;
     activeRefPosition = nullptr;
 
     // Get the value of the environment variable that controls stress for register allocation