LSR pass: disable support for unknown step

Disable by default following options:
 * EnableGEPLSRUnknownConstantStep
 * EnableGEPLSRMulExpr

(cherry picked from commit 3fc4609)

Author: pkwasnie-intel

IGC/Compiler/tests/GEPLoopStrengthReduction/optimize-mulexpr-with-high-regpressure.ll

@@ -7,7 +7,7 @@
 ;============================ end_copyright_notice =============================
 
 ; REQUIRES: regkeys
-; RUN: igc_opt -debugify --igc-gep-loop-strength-reduction -check-debugify -S < %s 2>&1 | FileCheck %s
+; RUN: igc_opt --regkey=EnableGEPLSRMulExpr=1 -debugify --igc-gep-loop-strength-reduction -check-debugify -S < %s 2>&1 | FileCheck %s
 
 ; Reduced index is expressed with SCEVMulExpr.
 

IGC/common/igc_flags.h

@@ -321,8 +321,8 @@ DECLARE_IGC_REGKEY(bool, RunGEPLSRAfterLICM, false, "Runs GEP Loop Strength Redu
 DECLARE_IGC_REGKEY(DWORD, GEPLSRThresholdRatio, 100, "Ratio for register pressure threshold in GEP Loop Strength Reduction pass", true)
 DECLARE_IGC_REGKEY(bool, EnableGEPLSRToPreheader, true, "Enables reduction to loop's preheader in GEP Loop Strength Reduction pass", true)
 DECLARE_IGC_REGKEY(bool, EnableGEPLSRAnyIntBitWidth, false, "Enables reduction of SCEV with illegal integers. Requires legalization pass to clear up expanded code.", true)
-DECLARE_IGC_REGKEY(bool, EnableGEPLSRMulExpr, true, "Experimental: Enables reduction of SCEV with mul expression.", true)
-DECLARE_IGC_REGKEY(bool, EnableGEPLSRUnknownConstantStep, true, "Experimental: Enables reduction of SCEV with step expressed with constant value unknown at compilation time.", true)
+DECLARE_IGC_REGKEY(bool, EnableGEPLSRMulExpr, false, "Experimental: Enables reduction of SCEV with mul expression.", true)
+DECLARE_IGC_REGKEY(bool, EnableGEPLSRUnknownConstantStep, false, "Experimental: Enables reduction of SCEV with step expressed with constant value unknown at compilation time.", true)
 DECLARE_IGC_REGKEY(bool, PrintWaveClusteredInterleave, false, "(Debug) Print if WaveClusteredInterleave pattern was found.", true)
 DECLARE_IGC_REGKEY(DWORD, FPRoundingModeCoalescingMaxDistance, 20, "Max distance in instructions for reordering FP instructions with common rounding mode", false)
 DECLARE_IGC_REGKEY(bool, DisableDotAddToDp4aMerge, false, "Disable Dot and Add ops to Dp4a merge optimization.", false)