GEP Loop Strength Reduction pass - don't truncate index type

Don't truncate index type when inserting new GEP instructions.

(cherry picked from commit f8a991b)

Author: pkwasnie-intel

IGC/Compiler/Optimizer/OpenCLPasses/GEPLoopStrengthReduction/GEPLoopStrengthReduction.cpp

@@ -817,7 +817,7 @@ void Analyzer::analyzeGEP(GetElementPtrInst *GEP)
         return;
 
     if (S->getType() != Start->getType())
-        Start = SE.getZeroExtendExpr(Start, S->getType());
+        Start = isa<SCEVSignExtendExpr>(S) ? SE.getSignExtendExpr(Start, S->getType()) : SE.getZeroExtendExpr(Start, S->getType());
 
     // Try adding reduction to existing group
     for (auto &c : Candidates)

IGC/Compiler/tests/GEPLoopStrengthReduction/three_accesses_addexpr.ll

@@ -45,8 +45,8 @@ entry:
   br i1 %cmp33, label %for.body.lr.ph, label %for.end
 
 ; CHECK-LABEL: for.body.lr.ph:
-; CHECK:         [[ZEXT:%.*]] = zext i32 %add4.i.i.i to i64
-; CHECK:         [[GEP_PHI1:%.*]] = getelementptr i32, i32 addrspace(1)* %p, i64 [[ZEXT]]
+; CHECK:         [[SEXT:%.*]] = sext i32 %add4.i.i.i to i64
+; CHECK:         [[GEP_PHI1:%.*]] = getelementptr i32, i32 addrspace(1)* %p, i64 [[SEXT]]
 ; CHECK:         br label %for.body
 for.body.lr.ph:                                   ; preds = %entry
   br label %for.body

IGC/Compiler/tests/GEPLoopStrengthReduction/two_accesses_licm.ll

@@ -33,8 +33,8 @@ entry:
 
 ; CHECK-LABEL: for.body.lr.ph:
 ; CHECK:         [[ADD:%.*]] = add i32 %delta, 2
-; CHECK:         [[ZEXT:%.*]] = zext i32 [[ADD]] to i64
-; CHECK:         [[GEP1:%.*]] = getelementptr i32, i32 addrspace(1)* %p, i64 [[ZEXT]]
+; CHECK:         [[SEXT:%.*]] = sext i32 [[ADD]] to i64
+; CHECK:         [[GEP1:%.*]] = getelementptr i32, i32 addrspace(1)* %p, i64 [[SEXT]]
 ; CHECK:         br label %for.body
 for.body.lr.ph:                                   ; preds = %entry
   br label %for.body